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Electricity Simplified 

THE PRACTICE AND THEORY 
OF ELECTRICITY 



INCL UDING A POP ULAR RE VIE W OF THE THEOR Y 
OF ELECTRICITY, WITH ANALOGIES AND 
EXAMPLES OF ITS PRACTICAL AP PLI- 
CA TLON IN E VER Y-DA Y LLFE 



tS BY 

T. O'CONOR SLOANE, E.M., Ph.D. 

AUTHOR OF 

Home Experiments in Science," " The Arithmetic of Electricity," etc. 



UllusfccatjexX 




NEW YORK 
NORMAN W. HENLEY & CO. 

150 Nassau Street 
1891 



rfl 



o? 



^A 



* 



Copyrighted, 1891, 
BY 

NORMAN W. HENLEY & CO. 



PEEFACE. 

It is a fair presumption that the modern develop- 
ments in the electric field, as generally understood, 
have occurred within the lifetime of the readers of 
this work. The achievements of engineers have pre- 
ceded theory, and to-day the latter is far in arrears, 
and seems likely to stay so. It is a peculiarity of 
mankind that it is most strenuous in seeking an ex- 
planation of the strange and unfamiliar. We are 
willing to spend a life, dependent in every physical 
sense upon gravitation, without once seeking its cause. 
But for electricity, in its aspect of a new and. strange 
creation of man's ingenuity, though in no way a 
greater mystery than gravitation, an explanation is 
required. 

To play a part in gratifying this desire is the ob- 
ject of the present work. A theory, which is far from 
complete has been constructed by modern scientists, 
and may eventually acquire perfect shape. The hy- 
pothetical luminiferous ether is at its base. The 



vi PREFACE. 

probable identity of species of electromagnetic and 
light and beat waves give us an additional right to 
use the ether in explaining these manifestations of 
electricity. This theory is treated here. 

It is the fashion to consider the ether a thing of 
proved existence, and to treat it's properties as quite 
within human conception. Neither practice is cor- 
rect. The existence of the ether has not been abso- 
lutely proved. Its properties are such as to remove 
it beyond the 'powers of conception of most or all 
of us. Edgar A. Poe's limitation of human intelli- 
gence applies well here. He says: " I doubt, indeed, 
whether the man lives who can force into his brain 
the most remote conception of the interval between 
one milestone and its next neighbor upon the turn- 
pike." 

The practical aspect has been kept in view. The 
use of analogies and the portions devoted to the en- 
gineering world will, it is hoped, prevent the reader 
from feeling that the work is purely on theory. Its 
object is to unite theory and practice. If this has 
been done, its mission is complete. 



CONTENTS. 



CHAPTER I. 

The Ether — Electricity — Force and Energy — Mass 
and Weight , 9 

CHAPTER II. 

The Electric Charge — Potential — The Dielectric — 
Positive and Negative Electricity — Contact Action — 
Electrostatic Lines of Force — The Ley den Jar.. ... 19 

CHAPTER HI. 

The Electric Current and Circuit — Relations of Elec- 
tromotive Force, Resistance, and Current — Velocity of 
Electricity 38 

CHAPTER IV. 

Fundamental Units and the Relations between Elec- 
trostatic and Electromagnetic Units — Practical Units ; 
the Volt, Ohm, Coulomb, and Ampere — Electric Force, 
Work, and Energy — Chemistry of the Current 54 

CHAPTER V. 

The Magnetic Circuit and Electromagnetic Lines of 
Force — Magnets and Ampere's Theory 76 



10 ELECTRICITY SIMPLIFIED. 

as representing and including special phenomena of 
this ether. Some go so far as provisionally to define 
it as being the ether itself, and to treat static excite- 
ment, magnetism, current electricity, etc., as due en- 
tirely to different states of the ether. 

The luminiferous ether is by calculation deduced as 
being of the following general properties. It is sup- 
posed to be a medium most resembling a gas in consti- 
tution, yet possessing rigidity like a solid, as well 
as elasticity like that of a gas. Its density is equal 
to 936 one-thousand-milHon-millionths (yrroVAow) 
that of water, or equal to that of air at 210 miles 
above the earth. Its rigidity is one one-thousand- 
millionth (tq o o 0*0 o o o o ) ^ na ^ °^ steel. It is sometimes 
compared to an all-pervading jelly, through which 
waves of light and other radiant energy and of electro- 
magnetism are constantly throbbing. Particles of or- 
dinary matter move through it without resistance. 
It interpenetrates the molecules of matter, and hence 
an air pump is entirely without effect upon it. There 
is no such thing as an ether vacuum (Daniel). It 
cannot be excluded from empty space. 

Such is the hypothetical luminiferous ether, an 
ultra-gaseous body possessing the properties of both 
a solid and of a gas. It should be looked upon as an 
expedient for the present, as something most useful 
in formulating theories, but unproved. A theory is 
often little more than a symmetrical skeleton to sus- 
tain our laboriously acquired collection of facts. The 



THE ETHER AND ELECTRICITY. 11 

test of the utility or perfection of a theory is its abil- 
ity to foretell what will happen under given condi- 
tions. It may be able to do this and yet be wholly 
fictitious. 

Light is radiated from one body to another across 
enormous intervals of space. The mind cannot con- 
ceive of one body acting upon another without some 
connecting medium. The same applies to gravita- 
tion and electricity. The ether originally invented 
to account for the transmission of light through dis- 
tances, of unknown degrees of immensity in the case 
of the heavenly bodies, has been found a useful factor 
in formulating a theory of electricity. ■ * 

If any object is excited electrically, every object 
within its range of action, that is to say, which is not 
screened from its effects, is also affected. This in- 
volves the same kind of action across a space as ob- 
tains in the case of light. It is termed radiant action 
and is a manifestation of radiant energy. Again, an 
electric current or the poles of a magnet produce 
magnetic effects in their vicinity upon objects not in 
contact with them. This involves action at a dis- 
tance also. 

These are among the reasons which have induced 
scientists to invoke the luminiferous ether to aid in 
explaining and accounting for electrical phenomena. 
As employed in the present work it will be found 
useful in enabling the mind to better formulate a 
theory of the science. Extraordinary as the idea of 



12 ELECTRICITY SIMPLIFIED. 

the ether may appear, it is evident that the modern 
achievements of electricity are just as strange. They 
are of such nature as to be entitled to an extraordi- 
nary line of explanation. 

The sun is at such a distance from the earth that 
it takes light over eight minutes to travel from its 
surface hither. The nearest of the fixed stars are so 
remote that in many cases days and years are con- 
sumed in the passage of light from them to us. If 
one of these bodies were suddenly annihilated we 
should see its light after it ceased to exist. The sun 
would seem to continue to shine for eight minutes 
and twenty seconds after its extinction We may 
even now seem to see stars which long ago ceased to be 
luminous, and distant suns may now be radiating 
light into space, which light will not reaches to 
show us a new star, for years to come. 

All this is so strange and deals with such infinite 
relations of quantities as regards distances and time 
that the luminiferous ether, viewed from such a 
standpoint, seems not too extravagant a conception 
to account for the high velocity and intensity of radi- 
ant energy. 

Pulses or waves of electric energy are found to act 
like light, to be capable of transmission through some 
bodies, of reflection from others, and of refraction and 
interference. The relations between electrostatic and 
electromagnetic units indicates a ratio corresponding 
to the velocity of light. These considerations give 



RADIAN 1 ENERGY. 13 

direct ground for utilizing the theoretical ether as a 
medium for the propagation of electrical disturb- 
ances. 

The term radiant energy is continually acquiring 
new scope in physics. Many phases of electrical dis- 
turbance fall under this heading. Others may be 
attributed to radiant force. 

The passion for unification at one time tended to 
obliterate the old distinction between static and 
dynamic electricity. Now a true basis for such divi- 
sion must be recognized and may to a certain extent 
be determined by the consideration of force and en- 
ergy. True static phenomena are phenomena of ether 
stress or of force; electromagnetic wave and current 
phenomena are related to ether waves or energy. 

Force, Energy, Mass, and Weight. 

Physical concepts, such as force, mass, energy, and 
other elementary things, have received within recent 
years much accuracy and definition of description 
and attributes. Only a few years ago great confusion 
existed, notably in the distinction between force and 
energy. The enunciation of the absurd doctrine of 
the conservation of force, and its support in many 
essays and papers by those who were assumed to be 
the leading thinkers of the day, is an illustration, now 
but a few years old, of this fact. 

This accuracy has led, and is leading, to more and 
more subdivisions, which brings about a multiplica- 



14 ELECTRICITY SIMPLIFIED. 

tion of units, and increase in nomenclature especially 
in electricit} 7 , which has already been felt to be a 
misfortune, although it is not easy to see how it is to 
be avoided. * 

For the purposes of this work it is quite unneces- 
sary to enter into all of these subdivisions. There are 
a few elementary mechanical ideas which may be 
enunciated before the electrical part is entered on. 
These involve subjects wdiich are often sources of 
error and misunderstanding. 

As physics and mechanics are based upon measure- 
ment, units of different kinds have been established. 
They are based upon length, time, and weight. The 
relations of these factors to the compound units are 
termed the dimensions of the unit. The centimetre, 
gram, and second are the bases of measurement, and 
the fundamental units constructed or built up upon 
them are termed the centimetre-gram-second or 
0. G. S. units. 

Force is that which, acting on a quantity of mat- 
ter or mass, can change its rate of motion or can im- 
part motion to it. It can be called into existence or 
annihilated under adequate conditions; in other 
words, there is no conservation of force. Its unit is 
that force which can in one second impart to one 
gram of matter a velocity of one centimetre per sec- 
ond. This unit is termed the dyne. The weight of 
one gram is equal to about 981 dynes. A dyne is 
equal to about : 63| grains. 



FORCE AND ENERGY. 15 

The exertion of force along a path in space, which 
condition necessarily implies motion against resist- 
ance, is termed work. Its unit is a dyne exerted 
through a path one centimetre long. The most con- 
venient way to express force is to refer it to gravita- 
tion. Hence the unit of work is generally denned 
as the raising of -^- f gram to a height of one centi- 
meter against gravitation. The name of the unit is 
the erg. 

The power of doing work is termed energy. A 
weight of t^t gram by frictionless machinery could, 
in descending one centimeter, raise another body of 
the same weight the same distance. Hence it would 
be said to possess en erg}" of position, a form of poten- 
tial energy, equal to one erg. The sum of energy in 
the universe is invariable; energy can be neither 
created nor annihilated by natural causes. This is the 
doctrine of the conservation of energy, which has re- 
placed the discarded one of the conservation of force. 

If a bullet is fired from a gun, the energy of the 
combustion of the powder is in part expended in 
driving the bullet forward ; in part in driving the 
gun backward, producing recoil; in part in heating 
the gun and bullet, and in various other ways. None 
of its energy is destroyed. The bullet strikes a tar- 
get and is brought to rest. Its energy is not de- 
stroyed, it is only transformed. Some appears as 
heat energy — indeed most of it directly or indirectly 
takes this form: none disappears. 



16 ELECTRICITY SIMPLIFIED. 

If this doctrine is true, perpetual motion against 
resistance, as generally understood, is impossible. 
There is very little doubt of this doctrine's truth. 

It follows from the above that energy cannot, prop- 
erly speaking, be expended, and that work is not done 
at the expense of energy. Work simply denotes the 
reciprocal of a given form of energy, and is produced 
by the disappearance of that particular form of energy, 
and is the result of its conversion into some other 
form. A weight raised by the combustion of coal is 
the reciprocal of the heat energy, and no more repre- 
sents work than it does the product or the result of 
the conversion of heat energy into mechanical poten- 
tial energy. In other words, work and energy may be 
treated as identical. To do work, energy is required, 
and is absorbed in the process by being converted into 
some other form or forms. The other forms, either 
one or more of them, are in many cases some irreclaim- 
able form or forms, which can never again be 
utilized. This is so often the case that the available 
energy of the universe is undoubtedly tending to 
zero. This zero will be attained when all objects 
have the same temperature. 

A body placed at a height above a plane possesses 
what is termed potential energy, referred to the 
plane. Its advantageous position indicates a power 
of doing work. Another example of potential energy 
would be a strained spring, possessing the energy of 
stress. 



ENERGY AND MASS. 17 

A body in motion, by virtue of its inertia or resist- 
ance to reduction of velocity, can do work, and is said 
to possess kinetic energy. A body at rest in a cer- 
tain sense may be said to possess the same with refer- 
ence to moving bodies, because all rest and motion 
are relative. 

An example of the transformation of energy can 
be taken from the above. A one-pound weight raised 
one hundred feet has expended upon it one hundred 
foot-pounds of energy, and possesses that amount of 
potential energy. If now it is allowed to fall through 
the same distance, it parts with its potential and as- 
sumes kinetic energy. When it has fallen one hun- 
dred feet, if in a vacuum, it will at the one-hundred 
foot mark possess none of its original potential en- 
ergy, but in its place will have one hundred foot- 
pounds of kinetic energy. As it strikes the ground 
and comes to rest, this energy will change into heat 
energy and other forms, but it will remain the same 
in amount — one hundred foot-pounds. 

Mass is the quantity of any portion of matter. 
Owing to centrifugal force a body weighs less at the 
equator than at the North Pole; upon the surface of 
the moon it would weigh far less. Yet its mass 
would be the same although its weight might vary. 
Were transportation cheap enough, and were the other 
conditions favorable, a merchant could make money 
by selling by weight, in northern or southern lati- 
tudes, goods which he had purchased by weight in 



18 ELECTRICITY SIMPLIFIED. 

equatorial latitudes, provided he weighed with a 
spring-balance. He would buy and sell the same 
weight, but would buy a greater mass than he sold. 

Weight is mass acted on by gravity. As gravity 
varies, weight will vary, even though the mass re- 
mains the same: all which has been just illustrated. 

In electricity we have force and energy. Heat en- 
ergy in driving an engine that drives a dynamo be- 
comes ultimately converted into electric energy. An 
electric machine or a battery on open circuit main- 
tains its terminals at a varying potential, or in such 
state as to exercise electromotive force. This force, 
producing a current through a resistance, does work. 
As for electric mass and weight, as yet they are not 
recognizable, and probably do not exist. 



CHAPTER II. 

THE ELECTRIC CHARGE — POTENTIAL— THE DIELEC- 
TRIC — POSITIVE AND NEGATIVE ELECTRICITY- 
CONTACT ACTION— ELECTROSTATIC LINES OF 
FORCE— THE LEYDEN JAR. 

The Electric Charge, Potential, and Dielectric. 

The first idea of electricity is that we are able to 
place bodies. in different electrical relations. A stick 
of sealing-wax or the amber mouthpiece of a pipe 
rubbed upon the coat sleeve will attract bits of pa- 
per, or will draw around with it, magnet-like, a 
walking-stick suspended by a thread tied around its 
centre. The very name electricity is derived from 
the Greek name for amber. 

The sealing-wax or amber in the above case is said 
to be charged with electricity, and represents the 
form of electric force already spoken of. It is use- 
less to attempt to determine what the electricity is 
whose presence so alters the condition of the body. 
It is usually taken as. an entity of some kind, and in 
old "times was termed and now is often termed col- 
loquially a fluid, although it is certain that it is no 
such thing. 



20 ELECTRICITY SIMPLIFIED. 

A body electrically charged is most simply treated 
as one whose surface is surcharged or undercharged 
with electricity. By an electric machine based upon 
contact action, by a galvanic battery, or by other 
means, electricity can be altered in its distribution. 
The action is analogous to that of a pump which 
pumps water from one reservoir into another, both 
originally of equal level. Thus we may imagine two 
reservoirs of similar level of water. If water is 
pumped out of one and into the other, they are 
brought into such relation that, if any chance was 
given, the water would flow from one to another, and 
the original level would be reached again. If for 
these reservoirs we substitute bodies insulated from 
any supply of electricity, we can by an electric genera- 
tor, which we may term an electric pump, abstract 
electricity from one and add it to the other. Both 
bodies are then said to be charged, one positively, the 
other negatively. As in the case of the reservoirs of 
water, if any chance was given, electricity would flow 
from one to the other, and the original state of things 
would be re-established. 

The electric charge resides entirely upon the sur- 
face; the cubic contents of the body has nothing to 
do with it. Again as regards a specific surface, there 
is no limit to the electricity which can be charged 
upon it, provided it can, so to say, be held there. 'By 
a physical metaphor, the elasticity of electricity seems 
to be perfect and indefinite. 



POTENTIAL DIFFERENCE. 21 

This gives the idea of an electric charge. Beturn- 
ing to our reservoirs of uneven level or " charged," if 
they were connected the original level would be at- 
tained, and more quickly or slowly in proportion to 
their difference of level. The greater this difference, 
the greater will be the tendency to return to the 
original level. The same applies to the electric 
charge. The greater the difference of charge, the 
greater will be the tendency toward partial equaliza- 
tion. This difference of charge is termed difference 
of potential, or potential difference, or electromotive 
force, and the terms high or low potential in a sys- 
tem indicate a large or small difference of charge 
of different parts. 

The levels of water in the reservoirs, instead of being 
compared with each other, might be referred to that 
of an ocean of constant level. Water might be 
pumped from one into the ocean, or from the ocean 
into one or the other, or both, so as to affect their level, 
with respect to such an ocea,n of constant height. 
Electricity can be treated in like manner. It can be 
pumped from the ocean of electricity, which the earth 
represents, or the same earth can be used as a recipi- 
ent of charges pumped from other bodies. Any of 
our reservoirs put into communication with the ocean 
would at once begin to attain the same level. Any 
charged electrical body put into communication with 
the earth, will in a short time, which may be an in- 
finitesimal fraction of a second, be reduced to the 



22 ELECTRICITY SIMPLIFIED. 

standard potential of the earth, which by convention 
has been taken as zero potential, just as in stating 
elevations of the earth's surface the height of the 
water of the sea is made the basis or zero of height. 

The fact that, other things being equal, the capac- 
ity of a body for holding- a charge of electricity de- 
pends upon the area of its surface is shown in a 
familiar experiment. If a piece of tinfoil or other 
conducting material is charged, and is then rolled up, 
thus reducing its area, the charge shows a higher 
tension or desire to escape. It is to a certain extent 
as if the area of one of our reservoirs was in some 
way diminished. The water would rise in height and 
acquire a greater pressure. This experiment also 
proves very clearly the fact that an electric charge 
resides upon the surface. 

Small drops of water charged with electricity, if 
they unite to form larger ones, will present a smaller 
total surface, and hence will raise the potential of 
their charge. This is supposed to be one of the 
causes of the electric disturbances in thunder showers, 
where the electric charge of the atmosphere seems to 
increase in potential enormously. 

The reservoirs, if to be filled or partly emptied, 
must have walls of some strength. If of the level of 
the ocean, their walls may be of zero strength for they 
will be supported outside by the ocean water which 
we may assume to penetrate the soil. To enable the 
surface of objects to hold an electric charge, they 



THE DIELECTRIC. 23 

must be surrounded by something to retain it. This 
substance or entity that holds a charge, upon a sur- 
face, which substance or entity represents the walls 
of the reservoirs, is termed the dielectric. It may be 
the air or any of the non-conductors of electricity. 
Even a vacuum is a dielectric almost equal to air. 
This fact is generally expressed by stating that the 
ether is a dielectric 

If connected by a pipe, the reservoirs will discharge 
one into the other and assume the same level. If 
two electrically charged bodies are connected by a 
piece of metal such as a wire, they will at once as- 
sume the same potential. The wire is termed a 
conductor. All metals and many other substances 
conduct electricity so well as to be termed conduc- 
tors. Others conduct it so badly as to be termed in- 
sulators. The latter are all capable of acting as 
dielectrics. 

If the air was a conductor, a surface could never 
be excited or charged in it, there could be no thunder 
storms, and man would probably have never known 
anything about electricity unless from animal sources 
such as the torpedo and gymnotus. Water contain- 
ing salt in solution is a conductor. Hence there are 
no electric storms or disturbances in the ocean and 
its inhabitants only experience animal electricity, but 
never that from any other source. 

The dielectric is the opposite of a conductor. Any- 
thing that is not a conductor may act as a dielectric. 



24 ELECTRICITY SIMPLIFIED. 

Formerly no distinction was drawn between it and 
an insulator. Now any insulator that surrounds a 
charged body, whether that insulator be glass, India 
rubber, gutta-percha, air, or a vacuum, is called a die- 
lectric. 

As the charge is to be held upon a surface, and not 
within a body, it is evident that for quick charging 
the surface must be conducting. Sealing-wax, am- 
ber, and glass, for instance, are non-conducting, and 
receive a charge only with difficulty, and part with 
it also with difficulty. If coated with tinfoil, gold- 
leaf, or some thin metallic coating, they become much 
easier to charge, although their capacity remains un- 
changed. 

This question of capacity is affected by two things, 
the area of the surface and the nature of the dielec- 
tric. The capacity of a system of two conductors 
and an intervening dielectric, called a condenser, is 
the quantity of electricity it can retain at a given 
potential. A typical form consists of two pieces of 
tinfoil with a sheet of gutta-percha, mica, or paper 
dipped in paraffin, between them. It is charged by 
passing or introducing opposite kinds of electricity 
into the two sheets of foil. As this is done the po- 
tential difference between the tinfoil layers rises, 
more rapidly as the surfaces are smaller, and this 
potential rise varies also very curiously with the na- 
ture of the dielectric. This difference between die- 
lectrics depends on specific inductive capacity. 



CONSERVATION OF ELECTRICITY. 25 

Positive and Negative Electricity. 

A zero of potential being accepted, arbitrarily taken 
as that of the earth, it is found that bodies can 
be excited so as to bear opposite relations not only to 
each other but also to the earth. This at once estab- 
lishes the idea of positive and negative electrical ex- 
citation, and of positive and negative charges. It is 
found that if a piece of glass is rubbed against a 
piece of amber they will become oppositely excited. 
As a matter of convention, the glassy or vitreous elec- 
tricity is called positive, and the resinous electricity 
is called negative. 

One body cannot be charged with a quantity of posi- 
tive electricity without an equal charge of negative 
electricity being established somewhere else, and vice 
versa. The algebraic sum of equal positive and neg- 
ative quantities being zero, the sum of all electrical 
charges in the universe is zero. This doctrine is 
comparable to the law of the conservation of energy, 
in the sense that the sum is constant, and it has 
been termed the law of the conservation of electricity. 

If copper and zinc are brought into contact and 
are separated, the copper is charged with negative, 
the zinc with positive, electricity. 

If the copper and zinc be immersed in acid which 
acts most strongly upon the zinc, the distribution is 
different: the zinc is negatively, the copper is posi- 
tively, charged. This is the case in a galvanic battery. 



26 ELECTRICITY SIMPLIFIED. 



k 



^This question of positiv e and negative gives the 
convention for fixing the direction of a curr enfD A 
current is assumed to be the discharge of positive 
upon negative. If negative electricity is poured into 
a body it adapts that body to receive a positive charge 
of equal value. 

All this is conventional; it is merely a necessity of 
the case. Some assumed direction of current and 
nomenclature of excitation is required. 

It will be observed that the relative conditions of 
zinc and copper are opposite when immersed in acid 
or when separated from contact. This is because 
when immersed in acid the excitation or charge is 
derived from the separation of the constituents of 
the water in which the acid is present. The hydro- 
gen with its positive charge travels to the copper; the 
other constituent atom of the water, or radical of the 
acid molecule, it may be, travels with its negative 
charge to the zinc. This negative charge it pours 
into it, or rather discharges it upon its surface, there- 
by adapting it to receive an opposite and equal charge 
of positive electricity from the copper. 

According to Franklin's views, who treated elec- 
tricity as a single fluid, the positive charge consists 
in an excess and the negative charge in a deficiency 
of electricity. Hence in the above illustration the 
zinc becoming negatively charged merely means that 
it loses a part of its total quantity of electricity. 
This carries out the idea of the direction of a current. 



SINGLE AND DOUBLE FLUID THEORIES 27 

The overflowing or positively charged body, namely 
the copper, sends a current, if permitted, into the 
partly exhausted or negatively charged body. 

Therefore, according to the single-fluid theory, a 
charge indicates an excess or deficiency according as 
it is positive or negative. It carries out well the 
theory of the conservation of electricity. 

The double-fluid theory assumed that there were 
two fluids, one positive and one negative, neutralizing 
each other in equal quantities. 

Now both these theories are discarded almost en- 
tirely. It is convenient as an analogy, however, to 
treat of electricity as a fluid in some of its manifesta- 
tions, and simplicity will be gained and the truth 
more nearly approximated to by using the single-fluid 
hypothesis where it gives a useful analogy. 

The charge, positive or negative, is really the key- 
note of all electrical phenomena. All that we know 
of electricity are the manifestations due to charges 
held upon surfaces and intermittently discharged, 
which is static electricity; or to charges continuously 
supplied and discharged along conductors, which is 
kinetic or dynamic electricity. The methods of pro- 
ducing these charges are by contact action and in- 
duction. To the first may be referred so-called fric- 
tional machines and also batteries. 

The relations of bodies oppositely charged in gen- 
eral are that the oj^posite electricities tend to com- 
bine. Bodies oppositely charged, therefore, attract 



28 ELECTRICITY SIMPLIFIED. 

each other. Under certain conditions they can im- 
part their opposite charges to each other and then 
are no longer attracted. 

The bodies excited oppositely as described and at- 
tracted cannot impart their charges one to the other 
through space, except where a conductor connects 
them, or, if not, where the charges are of high enough 
potential difference in relation to the space separating 
them and to the substance filling it. In that case they 
may discharge by a violent action producing a spark 
and noise. This disruptive discharge is seen in the 
lightning stroke. 

If the excited bodies are brought into contact, they 
will adhere, because the opposite electricities tend to 
combine. This adhesion, when satisfied, represents 
the disappearance of a specific form of energy. As 
energy cannot be annihilated, this specific form must 
be converted into some other, which other form is 
heat energy. The heat of combination of dissimilar 
metals, or of other substances, usually in the order of 
chemical energy and affinity, is also in the order of 
electrical energy. This correlates chemistry and elec- 
tricity. 

If, instead of bringing the bodies in contact with 
each other, they are connected by a metallic rod, their 
relative excitement disappears as long as they are 
thus connected. The rod acts to provide a path for 
the electricity and, as we have seen, is called a conduc- 
tor. The electricity passing by the path thus opened 



CONTACT ACTION. 29 

for it is termed a current. If one of the bodies is 
drawn away from the conductor, it has a charge pro- 
portioned to the difference of electrical character be- 
tween itself and the conductor. 

Just as the like poles of magnets repel each other, 
so two bodies excited with like qualitiesof electricity 
repel each other. 

If an excited body, for instance one with a posi- 
tive charge, is brought near an indifferent or un- 
charged body, it attracts it. This it does by attracting 
to the part of such body nearest it the opposite or 
negative electricity. This it attracts by attracting 
the body itself. If negatively excited, it also attracts 
by drawing the positive electricity of the body toward 
itself, and hence drawing the body as before. 

Contact Action and Electrostatic Lines of Force. 

Imagine two bodies of identical substance placed 
near together. A slight attraction will be exerted by 
each upon the other, which is termed the attraction 
of gravitation. Touch and separate them and the 
attraction will remain the same, and will vary, if they 
are small enough, in a certain proportion to their 
distance apart; if of small enough relative dimen- 
sions, with the square of such distance. Next assume 
two bodies of dissimilar nature placed near together. 
They will be attracted by mutual gravitation. * Now 
touch them, best by rubbing to secure good contact, 
and separate them, and they will exhibit a strong at- 



30 ELECTRICITY SIMPLIFIED. 

traction for each other. Under ordinary conditions 
this attraction will be vastly more than that of gravi- 
tation. A piece of sealing-wax rubbed against the 
coat sleeve will attract the sleeve. The contact acts 
to establish bonds of attraction that operate like India- 
rubber bands, pulling the two objects together. The 
objects are then said to be electrically excited. In 
this excitement and attraction not only the bodies 
but the intervening ether is thought to be concerned. 
The ether is supposed to be so stressed as to repre- 
sent or act like connecting India-rubber bands, and 
to pull the bodies together. The same applies to a 
magnet and its armature. The magnet throws the 
ether into an analogous state of stress. As its arma- 
ture is brought near it, this stress is affected by its 
proximity, and acts to draw magnet and armature 
together. As the stress is easiest pictured as con- 
necting lines, and as these lines indicate the exercise 
of force, they are termed lines of force, the first 
electrostatic lines, the others electromagnetic lines. 

There is no good analogy by which these phenom- 
ena can be pictured. Sometimes attempts in this di- 
rection are made by picturing the ether as composed 
of intermeshing cog-wheels. By using this concep- 
tion, various states of stress can be figured, but the 
examples do not seem very practical. 

The action of lines of force between excited disks 
or other objects is shown in the following illustra- 
tions. "When objects electrically excited with oppo- 



ELECTROSTATIC LINES OF FORCE. 31 

site electrical conditions are brought near together, 
the lines of force run almost straight from one to the 
other of the facing areas, while other lines curve 



Fig. 1.— Electrostatic Lines op Force Between Near Surfaces. 

around from the backs and sides of the objects. As 
they are more separated, the lines curve outward, al- 
ways tending to separate from each other, until the 




Fig. 2.— Electrostatic Lines of Force Between Distant Surfaces. 

conception of what occurs is what is illustrated in 
the second cut. 

The expression "lines of force" must be regarded 
as purely a matter of convenience. There are no 



32 ELECTRICITY SIMPLIFIED. 

real lines any more than there are individual and dis- 
tinct rays of light. 

This attraction of electrified bodies has been no- 
ticed for many centuries. The first observed electri- 
cal experiment on record is the attraction of rubbed 
amber for pieces of chaff. 

Unsatisfactory as these statements appear in the 
light of explanation, they are as satisfactory as any 
explanation of gravitation that can be evolved. But 
we are so familiar with gravitation that we do not 
stop to think about it, or to assign a cause for it. 

The Leyden Jar. 

The Leyden jar is a form of condenser. It is an 
apparatus for storing up a charge, or actually two 
equal and opposed charges of electricity. To provide 
conditions for doing this, a conducting surface is re- 
quired, to which should be added a second such sur- 
face, to hold an opposed charge of contrary name and 
to retain the original one as a bound charge. 

It consists of a jar of glass of good insulating 
quality, which acts as the dielectric. The interior and 
exterior surfaces of the jar over its bottom and half 
or two-thirds way up to its edge are lined with tin- 
foil pasted on. The foil provides the conducting 
surfaces to rapidly receive, hold, and rapidly discharge 
the charges. JThe glass above the foil is best shellacked 
or coated with sealing-wax varnish, to prevent con- 
densation of moisture. Such moisture would act as 



THE LEYDEN JAR. 33 

a conductor, and would provide an electrical connec- 
tion between the two surfaces of tinfoil. A rod ex- 
tends through the cork and connects with the inner 
coating. 

To charge the jar from a single source of electricity 
of high potential one coating is put into communi- 
cation with the source in question, and the other is 
connected to the earth. 

Electricity at once flows from the source to the 
surface connected to it, while the similar electricity is 
expelled from the other coating into the earth. Thus, 
as far as the earth is concerned, there might as well 
he no Leyden jar in the path of the current. As 
much electricity as flows into one coating is expelled, 
being the same quantity of the same name, from the 
other coating into the earth. The jar itself does 
nothing to disturb the balance. 

The process of charging goes on until the poten- 
tial difference of the two coats may be very high. 
On removing the jar, it is charged. One coating 
holds positive, and the other negative, electricity; 
both charges are bound to each other, and are exactly 
equal in amount. On touching or nearly touching 
both surfaces at once with the ends of a wire or other 
conductor, a spark will spring across and the surfaces 
will be nearly discharged. After a few minutes a 
second slight discharge (of the residual charge) can 
be taken from it. 

The Leyden jar, which in a certain sense bottles up 
" 3 



34 ELECTRICITY SIMPLIFIED. 

electricity, originated in an accident. An old-time 
experimenter, it is said, once approached or touched 
the prime conductor of an electrical machine with a 
nail protruding from the neck of a bottle containing 
water. The moisture on the outside of the bottle, it 
must be presumed, acted as an outer coating, and the 
water provided the same for the interior. On re- 
moving his bottle he received from it a violent shock. 
He had succeeded in putting electricity into a bottle. 

By arranging Leyden jars in different ways, the 
discharge can be made to vary in relations of quan- 
tity and intensity as in the case of a galvanic battery. 

If the jars are arranged with all the outside and 
all the inside coatings in communication, a large 
quantity of electricity can be accumulated. By ar- 
ranging them in series, the inside coating of one in 
communication with the outside coating of the next, 
and so on down the series, they will accumulate but 
a small charge proportional to the surface of a sin- 
gle jar, but of higher potential according to the 
number of jars in series. 

The difference of potential regulates .or determines 
the length of spark w T hich can be produced from 
given electrodes. When discharging a jar by inter- 
posing a conductor between the opposed coatings, the 
discharge always takes place before absolute contact, 
a spark appearing in the interval. By the length of 
this interval the length of the spark and with it a 
general idea of the tension is defined. 



THE FRICTION AL ELECTRIC MACHINE. 35 

The old frictional electric machine operates with 
the earth as a basis and charges the surface of its 
metallic prime 'conductor. Its general operation is 
exceedingly simple. A circular plate or a cylinder 
of glass is turned by hand. A cushion or pair of 
cushions are arranged in contact with the plate, so 
as to rub against it when rotated. These cushions 
are in communication by a metallic chain or other- 
wise with the earth. The contact brought about by 
friction and the constant separation of the glass 
surface from the cushions charges the glass with 
vitreous or positive, and the cushions with resinous or 
negative electricity. The prime conductor which is 
provided with a row or two rows of teeth, like a saw, 
nearly touching the glass as far from the cushions as 
possible, partly neutralizes the excited glass by com- 
municating to it a charge of negative electricity, thus 
remaining positively excited. Meanwhile the earth 
is absorbing the excess of negative electricity from 
the cushions as fast as it is produced by the rotating 
plate. 

If the reader will examine any of the old type of 
frictional machines he will readily follow out the 
above. 

The machine therefore establishes a charge in the 
prime condenser which, as its bound charge, has the 
excess in the earth. This sensitiveness of the earth 
to minute charges, strongly evidenced in the ground 
circuit of telegraph and telephone systems, is very 



36 ELECTRICITY SIMPLIFIED. 

surprising. The great sphere seems as sensitive to 
the smallest excess as to the greatest. 

Thus a person standing on the ground receives a 
spark from the prime conductor of a machine that 
has been worked. This indicates the rejoining of 
the excess of positive electricity on the surface of the 
prime conductor with the excess of negative elec- 
tricity on the earth's surface. 

The application of this to the Leyden jar is inter- 
esting. In charging a jar its inner coating generally 
is brought in contact with the prime conductor, and 
its outer coating communicates with the earth through 
the person holding it. 

The prime conductor communicates its charge to 
one coating, as just said, generally in practice the 
inner. The same quantity of the same kind of elec- 
tricity is expelled by induction from the other coat- 
ing of the jar, going to the surface of the earth. 
Thus the earth returns to neutrality as far as the ex- 
citement of the particular machine in question is 
concerned. The inner and outer coatings of the jar 
become oppositely excited, coming into the same re- 
lations as those originally existing between the prime 
conductor and the earth. 

Thus the two bound charges are separated only by 
thin glass, whereas when the prime conductor held 
a charge it was bound by the earth's charge. 

The full discussion of the Leyden jar involves very 
complicated calculations; and what has been said . 



CHARGING A LEYBEN JAR. 37 

only gives a very general idea of its operation. It is 
interesting to note its action in the charging process, 
when it conveys a charge to the earth by induction, 
although the jar has an insulating wall of glass be- 
tween its conductors. 

From the principles involved it follows that a Ley- 
den jar placed upon an insulator cannot be charged. 

There is a way in which a jar can be charged .with- 
out the intermediation of the earth. The coatings 
may be connected, each one to oppositely excited con- 
ductors. Each one is then charged from its respec- 
tive conductor. 

This systefii is followed in influence machines and 
may be used with induction coils. 



CHAPTER III. 

THE ELECTKIC CURRENT AND CIRCUIT — RELATIONS 
OF ELECTROMOTIVE FORCE, RESISTANCE, AND 
CURRENT— TELOCITY OF ELECTRICITY. 

The Electric Current and Circuit. 

When a body is charged with electricity we have 
seen that it indicates an equal and opposite charge 
somewhere else. The influence of an electrified body 
is to a certain extent like that of gravity — it may ex- 
tend everywhere through space. Just as a man theo- 
retically cannot leap from the earth without pushing 
the earth away from himself an infinitesimal dis- 
tance, so an electrified body may determine more or 
less stress in the most distant regions. 

If now a conductor is stretched from a region of 
one charge to a corresponding region of another op- 
posite charge, it separates or makes a tunnel in the 
dielectric, and the ether stress is relieved along the 
line of the conductor. The opposite electricities at 
once begin to neutralize each other by flowing along 
the path opened by the wire. 

"What part the wire and ether relatively play in the 
transmission of the electricity is still a matter of dis- 



THE CURRENT AND CIRCUIT. 39 

cussion. In all practical calculations and work the 
wire is assumed to be a direct conductor and the 
only thing concerned in the conduction. The pas- 
sage of the charges, if continuous, is called a current. 
Such passage to be continuous demands a constant 
supply of electricity, such as afforded by a battery, 
or a dynamo, or a constantly working electric ma- 
chine. 

The easiest and simplest analogy for a current is 
the flow of water. If we return to the reservoirs 
used as an illustration in preceding pages of this 
work, we find there the analogy of a current which 
equalizes two opposite charges. But it is obvious 
that to maintain a current from one reservoir to the 
other there must be some return path. This brings 
us to the conception of an electric circuit. Our 
water circuit must include what is virtually a return 
path, and so must an electric circuit. In some sense 
it must represent a complete cycle. 

A very familiar type of a circuit is given by a battery 
whose ends are connected by a wire. The current 
goes through the wire and, electrolytically, through 
the fluid of the battery. If the continuity is broken 
anywhere, there will be no current. When the cir- 
cuit is complete, a current passes. The continuous 
and complete one is called a closed circuit; the dis- 
continuous one is called an open circuit. The open- 
ing of a switch or release of a wire from a binding 
screw is enough to convert one into the other. 



40 ELECTRICITY SIMPLIFIED. 

If, in the hydraulic analogy the reservoirs be dis- 
pensed with, and a centrifugal pump in action be 
taken to represent a battery or dynamo, then a pipe 
connecting its inlet and outlet will represent a wire 
carrying a current. The system is complete in itself. 
If a hole were made in the pipe the water would not 
rush out, as the whole is self-contained. This is 
the case with a complete electric circuit. 

It is obvious that the pump might be kept in ac- 
tion by pumping from an ocean and back into the 
same ocean without disturbing its level. This would 
represent what is known as a ground circuit. 

It was an early discovery in the telegraphic world 
that a complete metallic circuit was not necessary, 
but that in common parlance the earth could be used 
as a return circuit. This type of circuit is repre- 
sented by a battery with a wire leading from one pole 
to any desired point, and then to the earth. From 
the other pole a second wire leads to the earth. It 
is immaterial on what part of the line the battery is 
i^laced. 

In this case the earth acts exactly like a conductor, 
with one difference : it has no resistance. 

No one can assert that the current in such a case 
really goes through the earth. One end of the line 
pours electricity of one kind into the earth. A cor- 
responding and exactly equal quantity escajDes from 
the earth at the end of the other conductor, and goes 
to the battery. It is simply the case of the pump 



THE ELECTRIC CIRCUIT. 41 

and the ocean over again. The earth acts as a great 
reservoir, and not as a conductor. Hence it is with- 
out resistance, just as the ocean would not have the 
resistance of a pipe. 

The action is the same as in the case of a.frictional 
electric machine just described. A centrifugal pump 
has been taken as the representative of an electric 
generator. Such a pump is peculiar in one respect 
as compared with piston pumps: if its inlet or out- 
let is closed, it does no work except such as is due to 
friction. To make such a pump run easily, the 
stopcock of the pipe leading from it should be closed. 
Then, were it not for friction, it would run on forever 
with but little absorption of energy, and would 
maintain a difference of pressure. Incidentally it 
may be noted that the closing of a stopcock consists 
in placing across the path of the water a substance 
through which it cannot pass, namely, a solid metal. 
The water current is surrounded by material of the 
same class, namely, the metal composing the walls of 
the pipe through which it flows. 

The battery or other electric generator operates in 
the same way. If its inlet or outlet conductor is 
closed by a substance through which the current 
cannot pass, it will, except for wasteful action, fric- 
tion, etc., maintain a difference of potential without 
absorbing energy or doing work. The closing and 
impassable substance may be any dielectric. Inva- 
riably in practice it is air. A switch is simply opened, 



42 ELECTRICITY SIMPLIFIED. 

which amounts to inserting a mass of air in the path 
of the current. The same dielectric in many cases 
surrounding the wire, as in telegraph lines, defines 
the path of the current, as the metal walls of a pipe 
define the path of a water current. Air in such a 
case represents to a certain extent the lead, iron, or 
brass of the water pipe, and represents exactly the 
metal of the plug of the water valve. 

The conductor of an electric current, though con- 
veniently pictured as a pipe, differs probably in its 
action therefrom. The ether surrounding it is sup- 
posed to be an active agent in maintaining the cur- 
rent; and the wire or conductor, while it carries the 
current also, enables the ether to do the work of 
pushing the current on its way. Thus some imagine 
a current not as determined by end action through 
a wire, but by a series of pushes or impulses commu- 
nicated through the ether outside the conductor, and 
localized by it all along its own line. 

Relations of Electromotive Force, Resistance, and 
Current. 

The cause of a current being the uniting of two 
charges opposite in quality, it is defined as due to a 
difference of potential. If such is maintained be- 
tween two points connected by a wire or other con- 
ductor which forms a path for a current, it obviously 
represents a kind of current-producing force, one 
which can keep electricity in motion against resist- 



OHM'S LAW. 43 

ance. It is for this reason also termed electromotive 
force, which for shortness is often written E.M.F. 

Electromotive force is the force maintaining or 
capable of maintaining a current through a conduc- 
tor. There is no perfect conductor known. Just as 
there is no frictionless conduit for water, so there 
is none for electricity. Force therefore is exacted in 
causing a current to flow through any path opened 
for it. The cause for this exertion of force is called 
resistance. 

In the case of currents the action of resistance is 
very simple. It restrains the intensity or strength 
of a current due to a given electromotive force, caus- 
ing more or less to flow through a circuit in simple 
proportion to the resistance itself. The three fac- 
tors, current, electromotive force, and resistance, are 
evidently interdependent. Their relations to each 
other are stated in the well-known Ohm's law thus: 
The current is equal to the electromotive force, di- 
vided by the resistance. This famous law is at the 
base of a large proportion of electrical calculations, 
and its applications are developed in treatises on the 
subject of the mathematics of the science. 

AVhile resistance thus affects the quantity of elec- 
tricity which flows under the action of a given elec- 
tromotive force through a conductor, it is without 
effect or action upon the velocity of transmission of 
an electric impulse. The facts that copper wire pos- 
sesses less resistance than iron wire and also trans- 



44 ELECTRICITY SIMPLIFIED. 

mits signals quicker have no inter-relation with each 
other. A small copper wire transmits telegraph sig- 
nals more rapidly than a large one, the latter of 
course being of much less resistance. 

If we take a wire through which a current is pass- 
ing, and examine its electrical condition, we shall find 
it a seat of electrical and thermal disturbances. It 
is a seat of energy, and as energy is expended on it 
it becomes heated. If by proper instruments we ex- 
amine the relative potentials of its different parts, we 
shall find a difference of potential existing between 
different places upon it, the differences of potential 
all falling in the one direction. This change of po- 
tential as it is expended in forcing a current through 
a wire is termed the fall or drop of potential. If 
the conductor is of uniform resistance, the fall of po- 
tential in any given portion will be in proportion to 
the length of such part of the wire. 

An excellent mechanical representation of the fall 
of potential is given by a wire subjected to twisting 
or torsion. The illustration shows an apparatus for 
carrying out this representation of an electric circuit. 
The vertical wire is supposed to represent a portion 
of a conductor. The twist which is given it repre- 
sents the electromotive force, and its degree is read 
off by the hands upon the dials. The weight which 
is sustained, by the lever at the bottom being turned 
slightly with the twist of the wire, represents the 
current intensity. If the wire is more twisted, it can 



POTENTIAL CTntRMJTT AJSD EFFICIENCY. 45 



support a greater weight. The twisting- is taken to 
represent electromotive force or difference of poten- 
tial, the increase of which factor 
maintains a greater current through 
a conductor or wire, which increased 
current is represented by the heavier 

On the wire the intermediate 
haH'is :"iS.=-.izir t-: siii: ~ = ir-:~~ ::-:.: 
on the amount of twist given the 
upper hand^ and proportional ex- 
to their distance from it. This 
ill - rra: cs :lir 1_;,~ :f :lir fall )f po- 
tentiaL In a conductor carrying a 
current the fall of potential in any 
proportional to the re- 
sistance of such part. Therefore if 
the conductor is of e - e n i action and 
:-rs:=:a^:--r :'..':: :_"!: ::.:. ulie lill ;■: 
potential will be proportional to the 

The decrease or fall of potential 
along an active circuit tends also to 
eliminate the idea of a current be- 
ing due to a simple end push. The 

electromotive force is present every- 
where in a circuit. The current 
is due to a determinable electromotive force in 
active circuit, and fractional parts of th-r 




Fig-. 3.— Xechanxc^i. 
IixrsTBATioy op Fall, 
op Potential asd Cub- 

L2TGTH. 



46 ELECTRICITY SIMPLIFIED. 

cuit are actuated by fractional parts of the electro- 
motive force. The portion of this total electromo- 
tive force expended in forcing the current through 
any section or division of the circuit is in exact pro- 
portion to the relative resistance of such section. 

As an example, a battery of ten units 7 resistance 
may be assumed as supplying an outer circuit of ten 
units' resistance also. Then one-half of the elec- 
tromotive force will be expended in overcoming bat- 
tery resistance, and one-half in overcoming the 
outer resistance. If the same battery supplies a line 
of one thousand units' resistance, the energy ex- 
pended in the outer circuit is equal to nearly T 9 „ 9 ¥ of 
the total energy. 

The efficiency of an electric generator is expressed 
by the resistance of the outer circuit alone, divided 
by the total resistance. In the last example this is 
given in the expression, 



or 99$ nearly. 

Such calculations are given in the mathematics of 
the science. The point to be established here is that 
relative resistances of conductors carrying constant 
currents define the expenditure of energy upon such 
conductors. The energy may appear as heat, as me- 
chanical work, or as chemical decomposition. The 
work done is due to a fall of potential along a con- 
ductor, and the fall is determined by the relations of 
resistances. 



DIAGRAMS OF CIRCUITS. 47 

The subject may be analyzed diagrammatically, 
remembering that the identical current goes through 
all parts of a circuit, and that all fractions of the line 
are subject to Ohm's law. Thus we may let a hori- 
zontal line represent the length of an electric circuit, 
say, 1,000 feet. At one end a vertical line may repre- 
sent the total electromotive force. Obviously, then, 
a diagonal forming the hypothenuse of the triangle 
will represent the average falling of potential down 
the line of wire or other conductor. 




LenqtA.<fa.Portuin of a. Circuit 

Fig. 4.— Diagram of Fall of Potential. 

But suppose that the line for equal lengths varies 
in resistance. Thus, assume that one-tenth the re- 
sistance is included in the first quarter, or 250 feet; 
then that 250 feet of fine wire are in the line, repre- 
senting one-half the total resistance; then that the 
next 250 feet represents one-quarter of the total re- 
sistance; while the remaining resistance, or fifteen 
one-hundredths, is in the next and last section of 250 
feet. Ohm's law tells us that the fall in potential 
varies with the resistance. Hence our diagram must 
show for the four parts of our line of 1,000 feet a 
fall proportional to the resistance of each section. 



48 



ELECTRICITY SIMPLIFIED. 



The diagram produced in this way is given here. 
The angle of inclination of the separate lines indi- 
cates the fall of potential or electromotive force ex- 
pended on each section. 

This gives a pictorial representation of the condi- 
tions obtaining in a circuit of varying resistance. 




Fig. 5.— Diagram of Fall of Potential in Different Parts of Circuit. 



We might go a step further and graduate the 
thickness of the inclined line to represent the resist- 
ance. As resistance is in opposition to the current, 
the line should he made thin for high and thick for 
low resistance, as in the next cut. 

The reciprocal of a number is the quotient ob- 
tained by dividing 1 by the number in question. 
The reciprocal of resistance is conductance. Hence, 
what was expressed in an indirect manner at the end 
of the last paragraph may be expressed directly in 
terms of conductance. The thickness of sections of 
the line may represent the conductance. This in 
the above case would give such a diagram as is given 
on the next page. 



VELOCITY OF ELECTRICITY. 49 

This diagram, which tells at a glance the whole 
story of the circuit, presents the analogy to a water 
conduit. The larger pipes manifestly require less 
head of water to convey the flow, and hence are rep- 



Fig. 6.— Diagram of Relations of Fall, of Potential and Resistance. 

resented less inclined. But the same quantity of 
water per hour or per second goes through all parts 
of the pipe, whatever its size. 

The Velocity of Electricity. 

The velocity .of propagation of an electric disturb- 
anc?, in the practical sense, is a variable quantity. 
The nature of the disturbance, and of the medium 
for its propagation, are all concerned in the question 
of the velocity of propagation of a signal. The fre- 
quent question, How fast does electricity travel ? 
cannot be broadly answered. If the ether is momen- 
tarily thrown into and released from stress, or if its 
condition of stress is changed suddenly, a wave is 
started, exactly as when a stone is thrown into a 
4 



50 ELECTRICITY SIMPLIFIED. 

quiet pond of water. This wave travels through 
space with the velocity of light, about 30,000,000,000 
centimetres per second, which is about 185,000 miles. 
Its velocity under all conditions as far as known is 
invariable. 

A wave travelling through space in all directions 
has a spherical front. On the surface of water a 
wave started by a stone has a circular front. But in 
going in all directions through space, the contour of 
any wave, such as an air or an ether wave, it is obvi- 
ous, is circular in all sections, or, what is the same 
thing, it is spherical. Hence its intensity diminishes 
rapidly, varying inversely with the square of its dis- 
tance from the point of origin. It is for this, as 
well as for other reasons, that the wave of electro- 
magnetic disturbance, with its high velocity of trans- 
mission, cannot be readily utilized in telegraphy. 
The difficulty of concentrating such a wave into par- 
allelism was to avoid the reduction of energy; and 
the interference of the curvature of the earth, coupled 
with the liability to interference with its path from 
other objects, has operated to render electromag- 
netic wave telegraphy of little practical use. The 
heliograph takes its place, with advantages of con- 
venience and simplicity. 

In practice the path of an electric disturbance or 
of the transmission of electric energy is determined 
by a wire or other conductor. The popular notion 
of the velocity of electricity is confined to the propa- 



VELOCITY OF SIGNAL TRANSMISSION. 51 

gation of a disturbance, such as a telegraph signal, 
along a conductor. Now into this disturbance many 
elements enter. The line has to be charged, as in 
ordinary land telegraphy, so that its capacity for 
holding electricity on the surface of the wire is con- 
cerned. All along the line of the wire the ether 
stress is changed. As the phase of stress runs down 
the line it advances like a wave, but like a wave the 
progress of whose full development is retarded. 

An uncharged line may be compared to a tube 
down which an impulse is to be given by a puff of 
air. A momentary blowing will send an impulse 
through the tube which will take a longer or shorter 
period to attain its full strength according to its ca- 
pacity, or according to the intensity of the blowing. 
Pneumatic tubes have been used to ring bells, the 
impulse being given by squeezing a bulb at one end. 
This compressed the air and sent an impulse down 
the tube, which rang a bell. 

It was at once found that the bulb had to have a 
large capacity compared to that of the tube, and 
small-bore tubes were naturally adopted for the pur- 
pose. In other words, small capacity of the pipe was 
found to be a great desideratum. It is precisely 
thus in electric telegraphy and general transmission 
of signals, telephoning, and other intermittent trans- 
mission. The smaller the capacity of the line, the 
better is the transmission of signals. 

The question in both cases, it will be seen, is not 



52 ELECTRICITY SIMPLIFIED. 

how fast a steady current passes through a line, but 
how long a wavelike disturbance will take, under 
specific conditions of line capacity and strength of 
original impulse, to attain a given intensity. 

In the case of the pneumatic signal tube and in 
the case of an electric telegraph the above condition 
exactly obtains. If one asks, How long does it take 
to send a signal across the Atlantic Ocean ? the ques- 
tion is thus interpreted by the electrician : An im- 
pulse being started through the cable, how long will 
it take such impulse to attain sufficient intensity at 
the farther end to actuate the receiving apparatus ? 
The elements entering are the electrostatic capacity 
of the line, the admissible strength of current that 
can be employed without injuring the cable, and the 
delicacy of the receiviDg instrument. 

Thus, starting with an uncharged Atlantic cable, 
if a current was suddenly started through it one-hun- 
dredth ( T fo") of the full strength would be felt at the 
farther end in about one-fifth of a second. Hence, 
with a delicate enough receiving instrument, this pe- 
riod would suffice for a signal to be transmitted. 
The current would go on charging the line of cable, 
and its intensity would increase at the farther end 
until, at the end of about 108 seconds, nine-tenths 
of its full strength would be felt at the distant end. 
With a very sluggish instrument used as a receiver, 
it is evident that even this period might be required 
for a signal to be sent across the ocean. 



SIGNAL TRANSMISSION. 53 

It is known that with fine-wire lines of small ca- 
pacity a signal can be transmitted with approxi- 
mately the velocity of light. 

The ether in its wave actions and impulses shows 
qualities comparable to inertia. In the case of a 
magnetic metal, such as iron, an electromagnetic 
action is produced by a suddenly started current 
which requires energy and hence retards the wave in 
its transmission. The electrostatic qualities of the 
dielectric surrounding the wire, air or gutta-percha 
or other material, also affect the velocity, as naturally 
does the size of the wire. 

It would seem that we would be justified in say- 
ing that in all cases the impulse would be trans- 
mitted in an infinitely small degree with the velocity 
of light. After this all the qualities and conditions 
named concur to determine the practical velocity of 
signal transmission. 



CHAPTER IV. 

FUNDAMENTAL UNITS AND THE RELATIONS BETWEEN 

ELECTROSTATIC AND ELECTROMAGNETIC UNITS 

— PRACTICAL UNITS I THE VOLT, OHM, COULOMB, 

AND AMPERE — ELECTRIC FORCE, WORK, AND 

' ENERGY — CHEMISTRY OF THE CURRENT. 

Fundamental Units and the Relations between 'Elec- 
trostatic and Electromagnetic Units, 

"When we do not know what a thing is, it is hard 
to conceive of a definite quantity of it. Bnt onr know- 
ledge of electricity is derived from its effects. From 
the measurement of its effects, therefore, we can de- 
fine a unit of quantity of electricity. 

When two equally electrified bodies, or bodies 
charged with electricity, attract or repel each other 
with a force of one dyne when one centimetre apart, 
each one is charged with a quantity of electricity 
fixed by C.G.S. units. This quantity is the C.G-.S. 
electrostatic unit of electricity. It is a perfectly de- 
fined unit, yet what it is that is measured is of course 
quite unknown. 

If two bodies repel or attract each other with some 
other intensity and at some other distance, the quan- 



ELECTROSTATIC UNITS. 55 

tity with which they are charged is easily determined. 
Suppose, for example, that a body charged with three 
units is attracted by one charged with six units. 
The total attraction of the six units of the second 
body for each one of the other three is obviously ex- 
pressed by six, giving a total attraction expressible 
by six multiplied by three, giving eighteen. 

The force, being a radiant one, varies inversely with 
the square of the distance. Hence, the attraction be- 
tween two bodies, at any distance apart, must be di- 
vided by the square of that distance to reduce the 
interval to unity, provided the area of the bodies is 
small enough to keep them under this law of radiant 
force. 

From these considerations the idea of different 
quantities can be conceived of. A body from its 
attraction for or repulsion from a definitely charged 
body — -that is, a body charged with a known quantity 
of electricity — can readily have the quantity of its 
charge determined. It is this supposed ether stress 
that gives the basis for determining the unit in 
question. 

If one C.G.S. electrostatic unit of quantity passes 
through a conductor every second, the current is of 
unit strength, and this is the electrostatic unit of 
current. 

If the work done by this current in one second is 
equal to one dyne of force exerted over a path one 
centimetre long, which is one erg of work, the 



56 ELECTRICITY SIMPLIFIED. 

potentials of the ends of the conductor differ by one 
electrostatic unit of electromotive force. 

If the conditions of the two suppositions of the 
preceding two paragraphs obtain, the conductor has 
one electrostatic unit of resistance. Any unit of cur- 
rent strength for electricity is such a unit as a gallon 
per second would be for water flowing through a 
conduit. Under the description of the ampere, more 
will be said upon this subject. The unit includes 
the idea of a definite quantity flowing per second of 
duration of the current. The electrostatic unit of 
current strength, often termed intensity, is therefore 
a current passing one of the units of quantity each 
second. If a current passes more or less, its intensity 
is determined by comparing it with the standard or 
unit current. 

It is evident that from a unit current the unit of 
quantity can be deduced. It is the quantity which 
such a current passes in one second. In this way 
the electromagnetic unit is obtained. It is, though 
indirect, the most natural way, because current elec- 
tricity is electricity in motion, and electromagnetic 
units are based on the latter form. The standard or 
unit current of the electromagnetic system is first 
determined, and from it the unit of quantity is de- 
rived, as given above. 

A unit current in the electromagnetic system is 
one which, passing through one centimeter of wire 
bent into an arc of one centimeter radius, exerts a 



RELATION OF FUNDAMENTAL UNITS. 5< 

force of attraction or of repulsion of one dyne upon 
a magnet pole of unit strength placed at the centre 
of curvature of the arc of wire. Such a pole is one 
which exerts one dyne attraction or repulsion at a 
distance of one centimetre upon a similar magnetic 
pole. 

Such current passes in one second one electro- 
magnetic unit of quantity. This deduction, it will 
be seen, is exactly the converse of the deduction of 
the electrostatic unit of current. 

When it is known that there are two complete sys- 
tems of C.G.S. electric units — one the electrostatic, 
the other the electromagnetic — based upon these two 
fundamental reactions, the interest and importance 
of their relation to each other is obvious._ The com- 
prehension of such relation also brings out the the- 
ory of electricity well, and gives a species of proof 
of the velocity of the electric current. It is a pity 
that it is not better understood, for certain difficul- 
ties attend upon the theory of its explanation. 

It is found that the electromagnetic unit of quan- 
tity is 30,000,000,000 times greater than the corre- 
sponding electrostatic unit. The explanation would 
be easy were electrostatic and electromagnetic lines 
of force identical in all respects; but it is definitely 
certain that they are not the same. An electrostati- 
cally charged body does not attract or repel a magnet, 
and a magnetic pole does not attract or repel an 
electrostatically charged body. Even this need not 



ELECTRICITY SIMPLIFIED. 

prove different ultimate and intrinsic qualities of 
the two kinds of lines of force. But we see no rea- 
son for believing, per se 3 that the electrostatic line of 
force is a series of molecular whirls or currents, such 
as the electromagnetic lines seem probably to be. 

It is generally believed that if a charged body were 
carried through space with sufficient, velocity, 
with the velocity of the electric current or of electric 
waves, it would act. as regards induction, like a wire 
carrying a current. 

The general statement of the relation of the two 
systems of units, and its connection with the velocity 
of propagation of ether waves, which may be waves 
of any form of radiant energy — light, heat, or elec- 
tricity — is this : 

The repulsive or attractive force of the centimetre 
of wire passing a unit current is equal to that of 
the unit electrostatically charged body. The same 
quantity of electricity is present in each; or one cen- 
timetre of wire passing a unit current contains, as 
long as the current passes, one electrostatic unit of 
electricity. The question now is. How many electro- 
static units of quantity pass through the wire per 
second ? Obviously they are as many as the centi- 
metres of wire which the current passes through per 
second. If all the assumptions made above are cor- 
rect, then the relation of electrostatic to the electro- 
magnetic units gives the velocity of electricity in 
current form. 



HYDRAULIC ANALOGIES. 59 

This may be made more clear by a recurrence to 
the hydraulic analogy. Suppose a pipe is of such 
size that one lineal foot of it contains a j>int of water 
when full. Si^ypose a current of water is going 
through it at a given number of feet per second. It 
is clear that the units of quantity, in this case jnnts 
of water, carried by such a current per second will 
be equal to the number of feet per second which it 
travels. 

The velocity of the electric current is supposed to 
be 30,000,000,000 centimetres per second. The electro- 
magnetic uuits of quantity and of current strength 
are as many times larger than the electrostatic units 
as the current travels centimetres per second. 

This view brings out the difference between the 
two modifications of electricity, the electrostatic and 
electrodynamic forms. One is electricity in repose, 
the other is electricity in motion. 

If, by trying the experiment, the length of wire 
passing an electrostatic unit current of electricity 
were determined, which wire would exert a dyne 
attraction or repulsion upon a unit magnet pole at 
unit distance, the length of such wire would give 
the velocity of the current. This would follow fron 
the fact that one electromagnetic unit of quality 
must be present at each instant, and always in the 
entire length of wire, since it exerts the force of one 
electromagnetic unit. It would be thirty thousand 
millions of centimetres lonsr. 



60 ELECTRICITY SIMPLIFIED. 

Thus, supposing our water pipe to pass one pint 
of water per second, the velocity of the stream would 
be equal to the length of pipe over which one pint 
was distributed. 

The velocity of light is found by experiment to be 
equal to 30,000,000,000 centimetres per second. This 
is the velocity of the electric current deduced from 
or explained in the above considerations. It is one 
of the reasons for believing light and electricity to 
be in the same order of forces, and is one of the 
grounds for the upholding of Clerk Maxwell's electro- 
magnetic theory of light. It justifies the use of the 
hypothetical luminiferous ether in explaining elec- 
tricity, as well as light. 

It is to be noted here that the velocity given above 
is more accurately defined as the velocity of propa- 
gation of an electromagnetic wave through the 
ether. The velocity of a current is really undeter- 
minable, except by the admission of some such hy- 
pothesis as the identity, in effect, of a current and of 
an electrostatically charged body moving with cur- 
rent velocity. 

Practical Units — tlieVolt, Ohm, Coulomb, and Ampere. 

We have already spoken of some fundamental 
units of mechanics. In practical work no one 
would use these numbers, on account of their incon- 
venient size. The same applies to electricity. There 
are the two complete series of electrical units, based 



PRACTICAL UNITS. 61 

on the centimetre, gram, and second, which have been 
described in part as examples of the fundamental or 
C.G.S. units, but which are not used to any extent 
practically. 

These two fundamental systems are the electro- 
static and electromagnetic systems of electric units. 

Taking the electromagnetic fundamental units as 
the primary ones, from them the practical units- are 
derived by the following process: Instead of being 
based upon the centimetre, gram, and second, the 
practical units are founded on the following quan- 
tities : (1) One thousand million centimetres, (2) the 
one-hundred-thousand-millionth of a gram, and (3) 
the second. In powers of ten these numbers are 
expressed briefly as follows: (1) 10 9 centimetre, (2) 
10~ n gram, (3) 1 second. The units are 10 9 0. 10- n G. 
S. units. 

If for the centimetre and gram we substitute these 
multiples of them, the practical units may be de- 
duced exactly as were the fundamental ones. There 
is a series of such units which threatens to become 
inconveniently long; but without entering into the 
mathematics of the science, some concrete idea of 
the meaning of the three most familiar of the prac- 
tical units may be given here. 

The volt is the practical unit of electromotive 
force, or of difference of potential. If we recur to 
our reservoirs of water, we should find a foot height 
of water a very convenient term to use as a unit of 



62 ELECTRICITY SIMPLIFIED. 

difference of height or of head of water. Such 
unit, one foot of head, is in constant use by all engi- 
neers. This is a precise analogy to the volt, which 
is the unit which measures the tendency of an elec- 
tric charge to escape to its opposite or bound charge, 
which tendency is the actuating force of currents, 
or is electromotive force. The volt is the cause of a 
current, but is not an attribute of it. It is the at- 
tribute of a circuit. The expression once so preva- 
lent, even with those supposed to be electricians, of a 
thousand-volt current or a hundred-volt current 
were incorrect and absurd. It would be almost as 
bad to speak of a thousand-pounds-to-the-square 
inch-flow or current of water. On the other hand, it 
would be correct to speak of a thousand-pounds-to- 
the-square- inch system of water-works or of a one 
thousand- or one hundred-volt electric circuit. 

A very familiar battery is the Daniell combination. 
It is made by immersing a plate of zinc in zinc sul- 
phate solution and a plate of copper in copper- 
sulphate solution, all in one vessel, the solutions 
being sometimes separated by a porous diaphragm. It 
can be seen in almost all telegraph offices in a 
modification called the "gravity" cell, in which the 
diaphragm is omitted. A battery is a contrivance 
which converts chemical energy into electrical energy, 
and which maintains a difference of potential between 
the surfaces of the opposite plates. The Daniell 
combination maintains a difference of one and seven- 



THE OHM AND AMPERE. 63 

one-hundredths volts between the surfaces of its 
plates. 

The unit of resistance is called the" ohm. Every- 
thing has electrical resistance. Some things have an 
almost immeasurable resistance, or offer an im- 
mensely powerful barrier to the passage of a current. 
Such are called insulators. Yet everything con- 
ducts to some extent ; and when an insulator is spoken 
of, it is only a relative term. The best insulator 
under the smallest electromotive force will carry a 
current. 

A column of mercury one square millimetre in 
cross-section and 1.0624 metre long has the resist- 
ance of one ohm. 

The practical unit of quantity is the coulomb. 

Take a conductor of resistance of one ohm, say our 
mercury column, and maintain a difference of poten- 
tial of one volt between its ends, and in one second 
one coulomb would pass through it. 

The practical unit of current strength or intensity 
is the ampere, also a much-abused term. It is the 
current of one coulomb per second, one which would 
be maintained through a resistance of one ohm by 
one volt potential difference between its ends. The 
combination just cited for the coulomb, therefore, 
involves a current of one ampere. 

A copper wire nine one-hundredths (yfg-) of an 
inch in diameter and eight hundred and thirty (830) 
feet long, connected between the terminals of a 



64 



ELECTRICITY SIMPLIFIED. 



Daniell cell of no resistance, which would be one of 
infinite size, would pass a current of one ampere. 
Such a cell is of course inconceivable. A dynamo 
of negligible resistance might easily boused to main- 
tain the requisite potential difference (1.07 volts) for 
the above wire. 

A greater potential difference will maintain 
through the same resistance an exactly proportion- 
ately greater current, and vice versa; a greater resist- 
ance will diminish the current in exact proportion, 
and vice versa. 

The ampere is a unit of rate, and the expression of 
one or ten amperes per second is redundant and useless. 




Fig. 7.— The Miner's Inch as an Analogy for the Ampere. 



The ampere is exactly analogous to a well-known 
unit of water flow, the " miner's inch/' This is a 
unit used by miners and irrigators in the Western 



THE MINERS INCH. 65 

and Pacific States. It denotes the rate of flow of 
water which, under a head of six inches, will pass 
through a hole one inch square in a board two inches 
thick. Let this head of water represent a volt, and let 
the resistance of the hole represent an ohm; then the 
miner's inch would represent a current of one 
ampere. One miner's inch per second or per hour is 
redundant, as everything is said when the simple 
" inch " is expressed. It may flow for a second or an 
hour. As we may speak of an " ampere-second/" a 
compound unit, which we have just seen is the 
coulomb, so we may speak of a "miner's inch- 
second," which is .1937 gallon of water. 

Electric Eorce, Work, and Energy. 

Energy and work in the mechanical world are in 
practice expressed in compound units, each composed 
of a unit of fall or rise multiplied by a unit of weight 
such as a foot-pound. Electrical work and energy 
are expressed in compound units each composed of a 
unit of quantity of electricity multiplied by a unit 
of fall or rise of potential. Thus energy is said to be 
expended in raising a quantity of electricity from 
a lower to a higher potential. 

The assertion is fair enough as an analogy, but it 
is often used as an expression of fact. This is going 
rather too far, unless the force of the expression 
" raising " be strictly limited to effecting a change of 
potential. 
5 



66 ELECTRICITY SIMPLIFIED. 

Taking a volt as the unit of potential and a cou- 
lomb as the unit of quantity, the volt-coulomb is 
the practical unit of electrical energy or work. 

Taking now, as before, a triangle as the repesenta- 
tion of a closed active circuit, we recognize in it two 
phases — one the expenditure of work, the other the 
expenditure of energy. Down the incline the ten 
units of potential, forcing a given quantity of elec- 
tricity per second through the resistance of the line, 
expend energy and do work. The work may appear 
as and be expended in the heating of material, run- 
ning motors, etc. The energy thus absorbed has 
to be supplied ; and this is done by the generator or 
battery, which doing work develops electrical energy 
up the perpendicular element, keeping to the tri- 
angle as a representation of the operations. 



The inclined path may be assumed to represent a 
road down which a carriage rolls. The broad lines 
represent a good road, the narrow lines a bad one. 



ANALOGIES OF CIRCUIT. 67 

To maintain a constant speed, it is evident that the 
inclination must vary with the quality of the road. 
Thus, the carriage will use up more or less of its 
energy of descent according to the quality of the 
track it follows, provided it is compelled, as is the 
electric current, to maintain a constant rate. 

After going down the incline, thereby expending 
its potential energy, the carriage has to be restored to 
its original position to repeat its course. This re- 
quires it to be raised up the vertical, which corre- 
sponds to the work of the battery in raising the fixed 
quantity of electricity back to its starting-point. 

The analogy is imperfect unless a series of car- 
riages, balls, or wheels perpetually going around the 
circuit is thought of. The flow of an electric cur- 
rent is continuous. 




Fig. 



A spiral line such as shown in the cut may be 
taken to indicate the fall of potential in a system ; the 



68 ELECTRICITY SIMPLIFIED. 

work of the battery will be represented by the verti- 
cal line. As the battery raises the potential, it is 
expended in the descent of the current down the 
spiral grade. 

Mechanical rate of work is measured by foot- 
pounds per minute, or by any other unit involving 
height, weight, and time. Electrical rate of work is 
measured by a unit involving potential difference, 
quantity of electricity, and time. Thus, taking the 
units we have been using, we have as a rate of work 
unit a volt-coulomb per second, which is the same 
as a volt-ampere. 

A mechanical horse-power is 550 foot-pounds per 
second; an electrical horse-power is 746 volt-cou- 
lombs per second, which is the same as 746 volt- 
amperes. 

The energy carried by a wire may seem an intan- 
gible thing, but it can be determined by a method 
simple in principle. When a wire carries a current, 
the fall of potential between its ends is determined 
by regular methods, as is also the current which goes 
through it. By multiplying the fall of potential by 
the current, the electric energy absorbed by the wire 
is ascertained. The heat energy corresponding 
thereto is ascertained by placing the conductor in a 
water or other calorimeter and determining the 
amount of heat units produced. 

On this or on a similar basis the efficiency of dyna- 
mos and other generators is ascertained. The energy 



CALORIMETER. 



09 



supplied to a mechanical generator, such as a dy- 
namo, is determined in mechanical units such as 
horse-powers. Then, it being known how many elec- 




Fig. 10. — Calorimeter. 



trical units correspond thereto and how many the 
dynamo produces, its efficiency is at once given. 



The Chemistry of the Current, 

An electrolyte is a liquid which is decomposible by 
the electric current and which necessarily is a con- 
ductor of electricity. 

An electric current which has an electrolyte in- 
cluded in its circuit effects a chemical decomposition 
of the electrolyte if the conditions are proper, or 
adapted for such action. These conditions are ab- 



70 ELECTRICITY SIMPLIFIED. 

solutely definite, and the decomposition can be 
exactly predicated of any given set of conditions. 

In a battery we see a decomposition effected, and 
the same action can be produced in another solution 
by a current produced by a battery or by any other 
means. It is easily illustrated in the experimental 
way by cutting a conductor at the desired place, and 
immersing its ends in the electrolyte. The electro- 
lyte is decomposed if the potential difference is great 
enough. The end by which the current enters takes 
the oxygen or corresponding portion of the sub- 
stance, while the other end takes the element corre- 
sponding to the hydrogen. 

The case of the decomposition of water may be 
taken. In a glass is placed water, made a conductor 
by the addition of caustic soda, sulphuric acid, or 
other compound not too easily decomposed itself. 

To the ends of the conductors plates or wires of 
some conductor not attacked by the decomposing 
electrolyte are attached. To produce a more rapid 
action it is well to make these large. If of wire, its 
exposed end may be wound into a coil. In dilute 
sulphuric acid plates of platinum are generally used ; 
in caustic-soda solution, iron acts excellently. 

The ends thus prepared are immersed in the water, 
and about two volts difference of potential are estab- 
lished between the two. As the current passes by 
electrolytic conduction, the water is decomposed into 
its constituent gases. From the end by which the 



DECOMPOSITION OF WATER. 



current enters, oxygen escapes; from the other, hy- 
drogen. The molecules travel, giving up One con- 
stituent to one electrode and the other to the second 
electrode as somewhat crudely shown here. They 



U 



Z3Z 



\* 







Fig. 11.— Theoretical Polarization and Decomposition of Molecules 
op Water. 

may he collected, if desired, in separate tubes or 
vessels, as shown. Although the water prepared 
for the experiment is a conductor, and can act as 
such with low potential difference, if the potential 
difference passes a certain point, absolutely fixed for 
water as well as for other compounds, but differing 
for each specific decomposition more or less, it acts 
as an electrolyte, and conducts electrolytically only ; 
it ceases to act as a common conductcr. The vol- 



72 



ELECTRICITY SIMPLIFIED. 



nme of gases given off is exactly proportional to the 
quantity of electricity passed by the current. 

By carrying out the decomposition in a closed 
vessel the gases will be set free and will accumulate 




Fig. 12.— Decomposition op Water by the Et.ectr to Current. 

under pressure. The most enormous pressures can 
thus be developed by the silent and unseen agency of 
the current. Two common gravity cells such as used 
in a telegraph office could burst a cannon shell. 
The decomposition is called electrolysis, and the 



ELECTROPLATING. 73 

immersed plates or ends are called electrodes. The 
plate attracting the oxygen is called the anode, the 
one attracting the hydrogen is called the cathode. 
All the nomenclature is rather cumbrous, and not 
very easy to remember. 

The same principles carried out for other chemi- 
cals brings about other decompositions. A solution 
of copper sulphate gives copper to the cathode and 
sulphuric acid to the anode. Silver cyanide in solu- 
tion gives silver to the cathode, and the decomposi- 
tion of an immense number of compounds have been 
elaborately investigated with regard to their heat of 
combination and decomposition, which are equal and 
equivalents, or rather reciprocals, of each other. To a 
definite heat of combination a definite voltage or 
potential difference corresponds. All these points 
have their place in the mathematics of electricity. 

The electrolyte, with its electrodes and cup con- 
taining it, when decomposed by a battery really rep- 
resents a second battery often in accord with the 
regular battery, as regards its polarity or direction of 
current, which it then would aid in producing. Some- 
times it acts against the battery, producing what is 
called counter-electromotive force ; and this condition 
is sometimes brought about after decomposition has 
been going on for some time. In the storage battery, 
from the start, the current it would produce is op- 
posed in direction to the charging current. Each 
cell has about two and one quarter volts counter-elec- 
tromotive force. 



74 ELECTRICITY SIMPLIFIED. 

By this principle of electrolytic decomposition the 
electroplating of surfaces is executed. The most 
varied effects and curious methods may thus be car- 
ried out. Of course its application to silver and 
nickel plating, as well as to other metals, is familiar 
and does not require mention here. 

Among the curious processes may be mentioned 
the electroplating of flowers and insects. By giving 
these a delicate coating of some material which will 
conduct the current, and attaching to them the wire 
from the zinc plate of a battery or from any source 
of electrical current, while the corresponding elec- 
trode is attached to the other wire, and by then im- 
mersing both in a proper solution, the object will be 
plated with silver, gold, or copper as the case may 
be, giving a beautiful metallic flower, leaf, or insect. 
The most varied objects, large and small, have thus 
been reproduced. Some have even gone so far as to 
suggest the electroplating of corpses, and it is cer- 
tain that a death-mask, as the sculptors call it, could 
be thus effectually produced. 

Another ingenious application has been proposed 
for making complicated and hollow objects. Copper, 
for instance, may be electrically deposited upon a 
core of a fusible alloy, and the core afterwards may be 
melted out. This has been proposed as a method of 
constructing Argand gas burners. 

Dissimilar substances such as platinum and carbon 
filaments can be connected by the electric deposition 



ELECTROLYTIC CONDUCTION. 75 

of a metal upon and over their junction, This pro- 
cess, termed electric soldering, is used in making in- 
candescent lamps. 

If an object is slightly oiled, the electric deposi- 
tion can be removed if the object is not "undercut," 
or is not of such shape as to prevent it. Thus a 
reverse of the object is produced, upon which as a 
model a second deposition can be made, giving the 
reproduction of the original. 

What is most striking about an electrolyte is that 
except for electrolytic conduction it passes no cur- 
rent. If enough potential difference is maintained 
between two electrodes immersed in it to effect its de- 
composition, the current it will apparently pass will 
be exactly porportional to the decomposition effected. 
For a given number of coulombs there will be pre- 
cisely a known weight of hydrogen set free if the 
solution is water, for instance. But the electrolyte 
must itself be a true conductor, and must have the 
power of actually conducting a current of lower po- 
tential. Thus chemically pure water is not an elec- 
trolyte because not a conductor. 



CHAPTEE V. 

THE MAGNETIC CIRCUIT AND ELECTROMAGNETIC 
LINES OF FORCE — MAGNETS AND AMPERE'S THE- 
ORY. 

TJie Magnetic Circuit, Electromagnetic Lines 
of Force. 

When two bodies are oppositely electrified, a stress 
is produced in the ether in their neighborhood which 
is represented by the figurative expression, " lines of 
force." Faraday's great work consisted in deter- 
mining the extent of the sphere of electrical action, 
showing that it was not confined to conductors, but 
that by far the most of it operated outside of con- 
ductors. Something has already been said of lines 
of force. A theory of the constitution of an electro- 
magnetic line of force may be here shown. The 
term electromagnetic lines of force has a definite 
meaning, which involves a distinction from electro- 
static lines of force. A magnet or a piece of steel 
which has been polarized is affected by the electro- 
magnetic stress, and tends to place itself parallel to 
its direction; and if the magnet is used, the north 
pole will always tend in the same direction with re- 
spect to the polarity of an electromagnetic line. 



ELECTROMAGNETIC LINES OF FORCE. 77 

The electrostatic line of force, on the other hand 
not affecting the magnet or iron filings, is evidently 
different in constitution. 

Because of their action upon magnets or iron filings, 
electromagnetic lines of force are more readily pic- 
tured to the mind. In this there is an element of 
danger, as the term "line" is only used as a matter 
of convenience. 

Unless otherwise specified, what is here said ap- 
lies only to electromagnetic lines of force. 

A line of force is supposed to represent the axis 
of a series of whirls of ether, which whirls are of molec- 
ular size. Thus, a series of curtain rings might be 
strung upon a stretched thread and caused to rotate 
around it. This would give some idea of the consti- 
tution of a line of force, and the thread would give 
its direction and its conventional representation as 
a simple line. 

The whirling of such a ring may be produced by 
stringing one or two curtain rings upon a piece of 
wire, which is then tightly stretched. On plucking 
the wire with the finger or sounding it with a violin 
bow, the ring will whirl around with extraordinary 
velocity, showing a very pretty figure by the reflec- 
tion of light from its bright surface. The same may 
be shown by a piece of string with a ring or even a 
button strung upon it. If such is stretched between 
the two hands, the same representation can be pro- 
duced. All this, of course, is merely a crude pictorial 



78 



ELECTRICITY SIMPLIFIED. 



representation or model of the supposed constitution 
of one of the whirls of an electromagnetic line of 
force. 

The direction and polarity of the lines of an actual 
magnetic field are easily studied. Without detracting 
from Faraday's unparalleled genius and work in this 
field, the ease with which electromagnetic lines of 
force can be mapped out and investigated conduced 
largely to the success of his investigations. 

Lines of force are studied most easily by the use 
of iron filings. These tend to arrange themselves 
parallel to and as nearly as possible in the axis of 
the lines. The field of force around a magnet is 
shown by placing a piece of paper over it, dusting 




Fig. 13.— Electromagnetic Lines of Force Shown by Iron Filings. 



ILLUSTRATIONS OF LINES OF FORCE. 79 

iron filings upon the paper, and tapping it. The 
filings take a symmetrical position, and show that 
lines of force connect the opposite poles of the 
magnet. An example of this experiment is shown in 
the first cut, and the diagrammatical representation 
in the next cut. 

' >>A\W////:::::::x\\\\i// / 







/til'. i', v \: — '>v'A'.",\ \\s 

Fig. 14.— Diagram of Paths of Lines of Force of a Bar Magnet. 

The circular lines of force which surround a wire 
carrying a current are shown by passing the wire 
through a horizontal card, upon which filings treated 
as above arrange themselves in circles. The diagram 
Fig. 18 shows the conception of the constitution of 
such lines of force, with their surrounding whirls. 

Lines of force possess several peculiar characteris- 
tics. One is that in air and most other mediums they 
are influenced by a tendency to separate from each 
other, but at the same time tend to take as short 
paths as possible. This separation is due to the fact 



80 



ELECTRICITY SIMPLIFIED. 



that air is a poor conductor for lines of force, or its 
permeance is low; hence they spread about in order 
to go through as large a mass of air as possible. 
Another characteristic is that in iron and in one or 
two other metals this diverging tendency is much 



&JUUUJSLSL*Jz i 




F^wL 



Fig. 15.— Experiment Showing 
Lines of Force Surrounding an 
Active Conductor. 



Fig. 16.— Diagram op Lines 
op Force Surrounding an 
Active Conductor. 



less marked; and if a piece of such substance be 
placed in the path of lines of force, a portion of 
them will crowd together into it, leaving their normal 
paths through the air for the better medium, iron, 
nickel, or cobalt. This is because the metals in 
question have high permeance for lines of force. 



THE MAGNETIC CIRCUIT. 



81 



Lines of force must go from somewhere to some- 
where. In the case of a magnet they go in a general 
sense from pole to pole, as shown in the cut. They 
are assumed, in the case of a magnet, to also go 
through the metal itself. They do not in this case 




Fig. 17.— Use of a Compass in Tracing Lines of Force. 



all emerge from the poles. A multitude of lines 
start from all parts of the magnet and enter at cor- 
responding points on the other side of its centre or 
neutral point. They may be traced by a small com- 
pass whose needle tends always to lie parallel with a 
line of force. 
6 



82 ELECTRICITY SIMPLIFIED. 

Every line, therefore, can be traced through a cir- 
cuit. The magnet with its lines of force represents 
what is known as a magnetic circuit. As magnetic 
polarization cannot be imparted to iron without 
creation of both north and south poles, and as a line 
of force starting from a north pole must return to a 
south pole, no magnetic lines of force can be estab- 
lished without the formation of a magnetic circuit. 

Here a difference from electrostatic lines of force 
appears. Every electrostatic charge k bound — that 
is, has an opposite and equal charge — somewhere. To 
this its lines of force go; but there is no circuit, there 
is only a connection. 

Lines of force in a magnetic circuit start from 
and return to all parts of the magnet except its cen- 
tre. All the parts of a magnet removed from the 
centre or neutral point have magnetism, and, if on 
different sides of the neutral point, are said to be of 
different magnetic potential, exactly as in the case 
of electric circuits. Hence this starting of lines from 
the sides as well as ends of the magnet is perfectly 
natural. 

The point is that only the centre of a regularly 
magnetized bar is without magnetism. If we go the 
least distance toward its north pole, starting from 
such central or neutral line, north polarity will be 
discovered, and the reverse if we explore toward the 
north pole. Difference of magnetic potential simply 
expresses the condition of any two points of a mag- 



CIRCULAR LINES OF FORCE. 83 

net at unequal distances from the neutral line, or at 
equal distances on opposite sides. A line of force 
starting from a point of given north polarity will 
return to a point of equal south polarity, but not to 
a point of higher or lower north polarity. 

The perfectly circular line of force is such as 
those surrounding a wire carrying a current. Its me- 
chanical analogue is seen in a smoke ring. These 
are easily made by cutting a hole in the 
side of a paper box, filling the box with 
smoke and gently tapping its side. This 
will cause smoke rings to issue, which 
have a whirling motion around the cir- 
cular axis of the ring shown in the dia- 
gram. Phosphureted hydrogen, inflam- 
ing spontaneously in air, shows the shape and rotary 
motion much better. Such are called vortex rings. 

The reason for asserting that lines of force have 
this electric whirl around them is that an electric 
current though a circular conductor creates lines of 
force within the area surrounded by it, and perpen- 
dicular to the plane of such circle. 

It is certain and evident that lines of force are 
maintained without the expenditure of energy. This 
would seem to offer a difficulty but for one thing — 
that we can assume that the electric whirls are of 
molecular dimensions, and that their current exists 
through a circuit of zero resistance, and hence repre- 
sent the expenditure of no energy. 




84 ELECTRICITY SIMPLIFIED. 

A curious coincidence and perhaps true analogy is 
to be remarked here. One of the attempts at figur- 
ing the molecules of matter has centred in the vor- 
tex ring, as it is called, which has just been described. 
This ring possesses various striking peculiarities 
which give it some resemblance to the supposed 
ultimate molecule of matter. Xow, in the electric 
world we find such rings, no longer of molecular 
size but only of molecular thickness, surrounding 
an electric current, and distorted lines of such whirls 
or rings emanate from and return to points of oppo- 
site polarity in a magnet. 

As, for the sake of convenience, a positive and neg- 
ative quality is attributed to electricity, and the di- 
rection of the current is assumed to be from posi- 
tively charged to negatively charged objects, so in the 
case of lines of force emanating from a magnet a 
direction is assigned to them. They are assumed to 
go from positive (north) to negative (south) pole of 
the magnet which creates them as indicated in the 
cut Eig 17. 

Magnets and Ampere's Tlieory. 

Every one is familiar with the magnet. It is put 
as a toy into the hands of children. It is found by 
them to attract steel; and if they go far in their exper- 
imenting they find that like poles of two magnets 
repel and unlike poles attract each other. 

It appears to be an endless source of energy, but 



THE MAGNET. 85 

this, of course, is impossible. It is a seat of force 
only, and in a certain sense can be made to store up 
or accumulate energy. The attraction and moving 
of its armature or other piece of iron to its polar sur- 
face requires the expenditure of energy. When such 
is drawn away from it, the work of so doing stores 
up energy in the magnet for the next attraction. 
If a magnet was made and allowed to attract an 
armature through a distance, its attractive force 
should theoretically be thereafter that much weaker, 
and no more, because separation of the armature 
would store up energy for the next attraction. But 
for the first attraction no special energy was stored. 

The fact that a magnet is not a seat of energy has 
not always been realized, and efforts are still made by 
inventors not conversant with electricity to utilize the 
magnet as a source of power. If this were possible, 
then perpetual motion would be discovered. Inqui- 
ries are often propounded as to what substance will 
cut off magnetic influence. This can only be done 
by some polarizable material which in itself will 
constitute an armature. The mere attraction of an 
armature and its retention only requires the exer- 
tion of force; the motion of an armature against a 
resistance such as its lifting through space re- 
quires energy. This distinction is important and 
too little appreciated. A magnet holding its arma- 
ture attracted does no work. 

When a bar of iron is wound with wire, insulated 



86 



ELECTRICITY SIMPLIFIED. 



or otherwise prevented from touching the iron and 
with its spirals not touching each other, the iron be- 
comes a magnet, It attracts iron and steel, each end 
repels one pole and attracts the other pole of a com- 
pass needle or other magnet, and it shows lines of 
force reaching from pole to pole and in general 




v^j^m. y 

Fig. 19.— Electro- Magnet Developing Lines of force. 



the indications of possessing magnetism or of being 
polarized. 

If instead of iron a piece of steel is taken and 
treated thus, the effects are the same in general, ex- 
cept that a large "portion of the imparted magnetism 
is permanent, and remains after the current has 
ceased. 

It is found also that the magnet thus made pos- 
sesses north and south poles, or, if suspended by a fine 
thread, or if floated on a cork on water, will point 



AMPERE'S THEORY. 87 

north and south approximately, and the same end 
will always seek the north pole and the other the 
south pole of the earth. The poles are found to be 
formed on one or the other end, according to the di- 
rection of the current which excited the bar to mag- 
netism. 

If the observer is imagined as facing one of the 
poles of a bar wound with wire as described, it is 
evident that the current may be supposed to go in 
the direction of the movement of the hands of a 
clock or watch — " clockwise"— or the reverse. If 
the current goes clockwise, then the pole facing the 
observer is a south pole. If the current goes against 
the direction of the clock's hands, then it is a north 
pole. This is shown in the cut Fig. 19. 

Thus, by varying the direction of a current, any 
polarity desired may be produced. 

When a magnet is thus produced, the lines of force 
are also formed with all their characteristics. There 
is absolutely no difference between a permanent and 
current-formed or electromagnet, except that the 
latter may be made much stronger than a permanent 
one. 

These facts give the basis for the famous Amperean 
theory of magnetism, devised by Andre Marie Ampere, 
the French scientist, from whom the practical unit 
of electric current- intensity is named. 

A permanent magnet is supposed to be a locus 
around which electric currents are perpetually circu- 



88 



ELECTRICITY SIMPLIFIED. 



lating in the direction of the hands of a clock if one 
faces the south pole or negative end. As a perma- 
nent magnet is not a seat of energy but of force, only 
the currents may be supposed to virtually consist of 
an aggregation of molecular whirls in circuits of no 
resistance, and of molecular size, exactly as in lines 
of force in the air or any medium. Thus the cut 
shows at A the north pole and at B the south j:>ole 
of a magnet, and a b and c represent the minute 
active circuits. 




Fig. 20.— North and South Poles of a Magnet to Illustrate Ampere's 
Theory. 

Two currents going in the same direction tend to 
place themselves parallel. The earth's polarity by 
the Amperean theory is accounted for by assuming it 
to be girdled by electric currents approximately in 
planes parallel to the equator, and going from east to 
west, opposite in direction to those encircling a mag- 
net whose north pole is pointing north. The ten- 
dency of the nearer portions of the two sets of circu- 



TERRESTRIAL MAGNETISM. 



89 



lar currents, one around the earth, the other around 
the magnet, to coincide in direction, and to be par- 
allel, causes the magnet to point north and south. 
The earth currents may involve the expenditure of 
energy, and probably do. Poor conductor as the sur- 
face of the earth may be, its interior may be better; 
and .in any case the great volume of the earth would 
compensate for its normally high resistance. 

As amber was the material with which the first 
experiment in static electricity was performed, and 
gave its name to the science, so the natural loadstone 
was the first magnet experimented with. It was 
found at Magnesia in Asia Minor, and the name 
" magnet " is derived from that of the locality. 




Fig. 21. 



If we follow out the fact that currents in the same 
direction attract each other, the same diagram will 
show that the opposite poles of magnets should attract 
each other for the same reason. The direction of 



90 ELECTRICITY SIMPLIFIED. 

the theoretical Amperean currents in a magnet being 
in opposite directions at the two poles, it is evident 
that when opposite poles are brought face to face the 
Amperean currents will coincide in direction. 

To an observer facing the north pole of the earth, 
the Amperean earth currents would seem to go in 
the direction of the hands of a watch. Thence it 
follows that, if the earth be considered a gigantic 
magnet, what we call its north pole would be really 
its negative or south pole. The confusion would be 
avoided if we call the positive pole of a magnet, the 
"north-seeking," instead of north pole, and vice 
versa. 

Again, if the earth is a magnet, lines of force should 
emanate from it, running from pole to pole, and 
from intermediate spots south of the magnetic equa- 
tor to points of equal potential north of the equator. 
Such lines of force have been proved to exist and by 
inductive action like that exercised by the field mag- 
nets of a dynamo upon its rotating armature a cur- 
rent is readily produced from them. The simple 
rotation of a coil about an axis properly placed is all 
that is necessary to produce a current. Such a coil 
is termed an earth coil and an example of one with 
galvanometer in the circuit is shown in Fig. 22. 

The lines of force should vary in intensity from 
the magnetic equator toward the magnetic poles, and 
a given earth coil rotated at a fixed rate should give 
different currents, those of greater intensity as it is 



MAGNETIC POLES OF THE EARTH. 91 



nearer to the magnetic poles. This is the case in 
fact, and is shown also in the varying directive power 
of the earth upon a magnet. 




Fig. 22.— Earth Coil. 

On the earth's surface matters would be simplified 
if the Amperean currents coincided with the parallels 
of latitude. Then the true equator would mark the 
neutral line or magnetic equator, and the magnetic 
poles would coincide with the poles of revolution. 
This is not the case, however. The Amperean earth 
currents are slightly irregular, so that the magnet or 
compass needle in placing itself at right angles to 
these currents will not, except at particular places, 
point north. Thus, the magnetic poles of the earth, 
determined by the intersection of verticals to the 
Amperean current lines, do not coincide with the 



92 ELECTRICITY SIMPLIFIED. 

true poles. The irregularity also is iu a perpetual 
state of change. 

The compass needle, in seeking the magnetic poles, 
also tends to leave the horizontal, or to " dip/' show- 
ing that the poles in question have their locus below 
the surface of the earth. 

A magnet, it is known, attracts a mass of inert iron. 
It does this by creating in it Amperean currents. 
Every piece of iron acted on by a magnet is for the 
time being a magnet itself. TThen iron filings are 
used to illustrate lines of force, or when a paper of 
tacks is emptied out upon a table, and is picked up 
by a magnet, every particle of iron is for the time 
being a magnet, its polarity being determined by its 
relation to the magnet. Each inplecule of the tacks 
or filings is the seat of an Amperean current. The 
same remark applies to filings used to show the cur- 
rent lines of force. Each filing is for the moment 
a magnet. 

Just as a magnet places itself at right angles to 
the earth currents, so it tends to place itself at right 
angles to artificial currents of electricity. Thus, a 
compass, brought near to a wire, indicates by its be- 
havior whether a current is passing through the wire 
or not. By referring its movement to the Amperean 
currents, and remembering that the effort is for cur- 
rents similar m direction to be parallel, the direction 
of the current can be told by the movement of the 
needle. Of course if the wire lies in the magnetic 



ACTION OF CURRENTS ON MAGNETS. 93 

parallel, it will be without effect on the compass 
needle, except to intensify or diminish its directive 
tendency. If it runs north and south and above 
the needle and deflects the north-seeking pole of 
the magnet to the east, then the current flows 
south; if to the w x est, it flows north. 

It is on this principle that most instruments for 
measuring currents, such as galvanometers, ampere- 
meters (or ammeters for brevity), and voltmeters, are 
constructed. The latter, although used for determin- 
ing potential difference, do it by measuring the cur- 
rent passing through their coil, and to that extent 
are amperemeters also. 

Some telegraph instruments, especially English 
ones, are based on this principle. Cable messages 
are often received by an instrument of this class, a 
reflecting galvanometer. 



CHAPTER VI. 

ELECTROMAGNETIC INDUCTION AND ACTION OF CUR- 
RENTS UPON EACH OTHER — THE INDUCTION 
COIL AND ITS APPLICATIONS. 

Electromagnetic Induction and Action of Currents 
upon Each Other. 

Induction is a phenomenon of action at a dis- 
tance which was spoken of in the "beginning of this 
work. A body receiving upon its face a charge of 
one kind of electricity immediately induces an oppo- 
site and equal charge somewhere else, which is bound 
to it by electrostatic lines of force. This is electro- 
static induction, and it continues as long as either 
body retains its charge or any fraction of it. Again, 
the attraction of a magnet for its armature, involving 
the conversion of that armature into a magnet for 
the time of contact or influence, is a form of induc- 
tion. Both these are examples of the exercise of 
force by induction ; in electromagnetic current in- 
duction we frequently deal with the exercise of great 
energy by induction. 

If a wire through which a current is passing lies 
near to and parallel with part of another wire, which 



ELECTROMAGNETIC INDUCTION. 95 

last-named wire is bent into a complete or closed cir- 
cuit, no action takes place unless the current strength 
in the first wire is varied, or the distance between 
the wires or their relative positions are altered. Then 
a momentary current at once is excited in the sec- 
ond wire. This is electromagnetic current induc- 
tion. 

Further than what has been said, nothing need be 
said about electrostatic charges and electrostatic in- 
duction. Electromagnetic induction is of more im- 
portance in the practical world, and will be spoken 
of here. 

It is the form of induction which owes its exist- 
ence to electromagnetic lines of force, such as those 
which have already been spoken of. 

Electromagnetic induction is of importance in the 
every-day world, because upon it depends nearly all 
the recent work in electricity. The immense devel- 
opment of the science witnessed in the last two dec- 
ades is due to the development of apparatus based 
on this particular form of induction. The single 
fact that dynamos and motors depend upon it for 
their action shows how practical a thing it is. 

In this chapter, when the word induction is used 
without qualification, electromagnetic induction will 
be meant. 

The first conception of induction may be taken 
from two parallel wires conducting currents. They 
may attract or repel each other, but will never be 



96 ELECTRICITY SIMPLIFIED. 

neutral. As we have seen, both are surrounded by 
ring-shaped or annular lines of force, of definite 
polarity, dependent on the direction of the current. 

If the current in both wires is in the same direc- 
tion, they will attract each other. This attraction 
may be referred to the annular lines of force. A 
moment's reflection, even without the aid of any dia- 
gram, will show that the portions of the lines of 
force nearest each other are of opposite polarity. 
Each annulus being of like total polarity, tangential 



s v^=^ 



/ ^y/ s/jtyy 



hH-r i-n-x — >} I 






Fig. 23. — Attraction of Conductors Carrying Similar Ccrrexts. 

portions are of opposite. Two wheels rotating in 
the same direction, if brought together, will have 
the portions of their peripheries which are in con- 
tact moving in opposite directions. 

This appears as a case of unlike attracting unlike. 
•If the attraction of the two similar currents for each 
other is referred to their lines of force, the phe- 
nomenon of attraction reminds us of electrostatic 
attraction. In the latter unlike attracts unlike. In 



REACTIONS OF ACTIVE CONDUCTORS. 97 

the attraction of similar currents the attraction of 
unlike for unlike is found in the contiguous por- 
tions of the lines of force surrounding the two wires. 

If, on the other hand, the currents in the two wires 
are of opposite directions, they will repel each other. 

Again picturing the annular or ring-shaped lines 
of force, it will be seen that the contiguous portions 
of these lines in the case supposed will be of identi- 
cal polarity, so that the phenomenon reduces itself 
to a case of repulsion of like by like. 

" ^.jj \^j) {^y j 

Fig. 24.— Repulsion of Conductors Carrying Opposite Currents. 



Thus, the apparent exception to the rules of likes 
and unlikes which is presented by wires, in which 
like currents attract and unlike repel each other, 
when reduced to phenomena of lines of force 'disap- 
pears. The general electrostatic law applies to the 
lines of force surrounding current -bearing conduc- 
tors. These lines appear subject to it, while the cur- 
rents are not. This is as it should be, because attrac- 
tion and repulsion are due to ether stress which is 
7 



98 



ELECTRICITY SIMPLIFIED. 



expressed in lines of force, as regards its direction 
and polarity. Again, we find in the repulsion of 
lines of force of like polarity a version of the spread- 
ing out of lines which has already been spoken of 
(pp. 79 and 80). In the attraction of lines of 
force of opposite polarity we find the reverse state 
of things,, as might naturally have been anticipated. 
These are two of the fundamental phenomena of in- 
duction. 

If now we take a single wire and bend it into a 
spiral, and pass a current through it, the annular 




Fig. 25.— Active Spiral Conductor Developing Lines of Force. 

rings will blend, and approximately elliptical ring- 
shaped lines of force will be produced. Eesistance 
has been spoken of in connection with currents. It 
has its analogue, called reluctance, in connection 
with lines of force. These go more easily through 



FIELD OF FORCE. 99 

some substances than through others. Iron, nickel, 
and cobalt are good vehicles for lines of force, or 
have low reluctance. Other materials have higher 
reluctance, and vary but slightly from air as regards 
their degree of the same. 

The coiled wire maintains a set of lines of force 
of rather low intensity, forming a magnetic field. If 
now a piece of iron is inserted in the coils, the field 
will be greatly intensified, because of the good vehi- 
cle for the transmission of lines of force provided in 
the iron. The magnetic field becomes very dense. 
Iron possesses low reluctance. 

Electrostatic lines of force pass out into space 
until they meet opposite ones. Electromagnetic 
lines, on the other hand, always return into them- 
selves. This gives the idea of a magnetic circuit. 
Every line of force of the electromagnetic kind in- 
cludes the idea of a magnetic circuit closely analogous 
to an electric circuit. 

The field of force created by coiled wires bearing 
currents, and strengthened in their action by an iron 
core, is the one used practically in dynamos and mo- 
tors. This field of force is no impracticable, dry ab- 
straction; it is at the basis of the action of every 
dynamo. All the electric lights and other powerful 
manifestations of electricity are due to the mainte- 
nance of such fields of force. 

A typical magnet, with the direction of its lines 
of force, is shown in the diagram Fig. 14. The 



100 ELECTRICITY SIMPLIFIED. 

idea of a magnetic circuit is very clearly shown here. 
The analogy with an electric circuit (generator and 
conductor bearing a current) is so good that the 
most practical calculations of electromagnets are 
based upon laws similar to Ohm's law, and embody- 
ing exactly similar ideas. 

Iron, having little reluctance, always concentrates 
in itself lines of force. The attraction of a magnet 
for its armature, or for any piece of iron, may be 
based upon the desire of the lines of force to take as 
good and short a path as possible. Their path is 
improved and shortened when the armature is in 
contact with the pole; hence the attraction of the 
magnet therefor. 

Thus, we have examined, although superficially, 
two typical cases' of lines and fields of force. The 
next step is to see how a current can be generated 
by the agency of such a field. 

If two wires or conductors are placed close to- 
gether, of which one only carries a steady current, 
the second wire will show not the least effect. But 
if the current in the other wire be varied in intensity 
or direction, then momentary currents will be in- 
duced in the other if its ends are joined so as to form 
a closed circuit. 

A theory or picturing of this is easily conceived 
of. It seems perfectly obvious that any disturbance 
of the lines of force which represent ether stress, 
and do not represent 'ether motion or ether waves, 



INDUCTION OF CURRENTS. 101 

will disturb the ether near them. The adjacent wire 
opens through the ether a path for a current. Hence 
the disturbance of the lines of force, involving waves 
of motion of the ether, establishes, as if it were by a 
species of sympathetic or harmonic vibration, a set 
of circular lines of force around the axis determined 
by the path through the ether opened by the other 
wire. But the forced establishment of these lines of 
force entails a current through the conductor in 
their axis, because lines of force and currents are so 
intimately connected that one cannot exist without 
the other, and disturbance of or creation of lines of 
force always affects a current. The creation of new 
lines of force around an idle closed-circuit conductor 
cannot take place without the production of a cur- 
rent. Lines of force proper to a conductor cannot 
exist without an accompanying current. 

The new lines of force are only determined by the 
change in the primary ones, and only exist while 
such change is taking place. Hence an induced cur- 
rent is of very short duration, and a steady current 
can only be produced by a continuous disturbance. 

A disturbance in the inducing conductor in the 
direction of increased strength of current gives the 
lines of force an extra thrust, as it were, and they 
tend, as if by cog-wheel action, to give the new lines 
of force around the neighboring wires opposite polar- 
ity. This entails a similar direction of polarization 
in contiguous parts, so that the two sets repel each 



102 ELECTRICITY SIMPLIFIED. 

other. This is merely another way of saying that 
the currents are in opposite directions, something 
which would follow from the opposite polarization of 
the lines of force. 

A disturbance in the direction of decreased strength 
of current, by letting the polarity of its circular lines 
of force diminish, gives a twist in the opposite direc- 
tion to the ether in contact with them. This in- 
duces lines of force around the adjoining wire of 
similar circular polarity. Hence, the new and old set 
of lines of force, having their contiguous portions of 
unlike polarity, attract each other, and, as the circular 
polarity is identical in both sets, the currents, original 
and induced, are in the same direction. 

All this coincides with the explanations given on 
pages 96 and 97. 

If we think of the circular lines of force in ac- 
quiring or losing intensity as being subjected to a 
virtual acceleration or retardation of polarization 
corresponding to a species of rotation, it will appear 
quite evident that they should thus affect the 
contiguous embryonic lines of force localized by a 
neighboring closed circuit. We have to imagine the 
circular lines of force as indicating the direction of 
a circular stress in the ether. 

From a magnet's face and sides the magnetic in- 
fluence or lines of force proceed in lines not very far 
from straight in the immediate neighborhood of the 
pole. If the magnetic force is constant, there are 



INDUCT WW OF CURRENTS. 



103 



no ether waves, but only ether stress, and no current 
can be induced. If a wire of a closed inactive cir- 
cuit is moved among these lines of force, it is sub- 
jected to ether stresses varying in intensity, which is 
another way of producing 
the effect of waves. As 
if by a species of friction 
against the lines of force 
of the magnetic field, the 
circular lines of force 
around the wire are de- 
veloped as before, and a 
current is started through 
it. If the wire is approach- 
ing the pole, it is the same 
as if a wave due to in- 
tensification of current 
met it, and lines of force 
of opposite sense are pro- 
duced, or an inverse cur- 
rent. If preceding from 
the pole, exactly the op- 
posite effect is produced. 
Again, we may take two 
bobbins, one A having a 
steady current passing around its coils, the other B 
ready to receive a current. If the inductor bobbin 
A is approached by the bobbin B, it is clear that 
lines of force of the direction a, a will thrust against 




Fig. 



-Generation of a Current 
by Induction. 



104 ELECTRICITY SIMPLIFIED. 

the ether surrounding B, and we m&y imagine a ten- 
dency to force new lines into the direction b, b. The 
currents of the windings of the bobbins, correspond- 
ing to lines of force of opposite polarity, such as 
shown, are obviously of opposite direction themselves. 
This means that if B approaches A a temporary cur- 
rent will be induced in its coils, of opposite direction 
to that in B. If drawn away, then obviously the op- 
posite effect should follow, and does follow. Lines 
of force of identical direction are produced, with a 
consequent current of the same direction, as that 
of the current in A. 

Two things are to be remembered: The current 
is induced in a closed circuit; no induction takes 
place without a change in the stress of the ether sur- 
rounding the induced wire. This change may take 
the form of a wave, or the motion of the induced 
wire may produce a wave effect, and give the desired 
thrust, or whatever it may be, that determines the 
formation of lines of force and of a temporary in- 
duced current. 

Recurring to the bobbins A and B, they may ap- 
proach in arcs or circles or in any way, but the mo- 
tion may always be resolved so as to give a resultant 
indicating approach or recession. From this the 
direction of the current can be told. The law by 
which it is regulated is. known as Lenz's law, which 
may be thus expressed : The induced currents are 
such as to develop resistance to the change brought 



LENZ'8 LAW. 105 

about. Thus, approach develops an opposite cur- 
rent because opposite currents resist approach, while 
recession develops a current of similar direction 
because similar currents attract each other. Start- 
ing or intensifying a current produces effects cor- 
responding to approach, and stopping or diminish- 
ing a current corresponds in effect to recession. 

The direction of lines of force can be mapped out 
by iron filings or by a compass needle. Thus they 
seem to the mind to have some real existence. The 
reactions among themselves have to remain little 
more than a metaphor, and this metaphorical pres- 
entation of the subject is for the present about all 
that can be done to give the mind some picture of 
the induction of currents. 

The Induction Coil and Its Application. 

It is a simple matter, on the principles just de- 
scribed, to produce high-tension electric charges in 
small quantity from low-tension charges in large 
quantity or to do the reserve. A stick of sealing-wax 
rubbed against the coat sleeve may give a higher ten- 
sion than an enormous dynamo. The old-fashioned 
frictional electric machine is based upon this prin- 
ciple. The trouble with the frictional machine and 
its successors, the influence machines, Holtz and 
Wimshurst types, is that they produce high-tension 
charges, but the current is apt to be intermittent 
and of very small quantity. Induction coils were 



106 ELECTRICITY SIMPLIFIED. 

designed to act as a substitute for f fictional ma- 
chines. They provide a comparatively constant dis- 
charge through air, and can be modified so as to give 
any ratio of currents and tension. 

The induction coil has received most important 
applications recently. It is the controlling element, 
used in the exact reverse of its original action, in al- 
ternating-current lighting, and it has been used in 
another application, also the reverse of the original, 
for producing a current adapted for electric weld- 
ing. 

The action of a wire, through which an alternat- 
ing current, or other current suddenly varied is 
passed, upon a neighboring circuit partly parallel 
thereto, has already been explained. The induction 
coil is simply an extension of this idea. 

A bundle of straight iron wires laid together may 
be taken as the core upon which an insulated copper 
wire is wound. If a current is passed through this 
coil, it will create lines of force, which will be con- 
centrated by virtue of the presence of the iron. 

Such an arrangement is called a spark coil, and 
is in itself sufficient to give a high enough tension 
to produce a spark. If the excited circuit is sud- 
denly opened or shut, a spark will appear at the 
point of " make and break." The electricity heaps 
itself up, as it were, and by a species of electric inertia 
accumulates tension enough to jump across the 
interval if not too large. For a fair-sized spark the 



THE INDUCTION COIL. 107 

conducting wire must have plenty of convolutions, 
and a good iron-wire core is essential. The phe- 
nomenon is attributed to self-induction, each convo- 
lution acting upon the others as if they were in in- 
dependent circuits. 

The sparking seen sometimes in telegraph instru- 
ments is due to the magnets acting as spark coils. 

The induction coil is an extension of the simple 
spark coil. Around an iron core is wound an in- 
sulated copper wire provided with an arrangement, 
like a little hammer and anvil, or some equivalent, 
for very rapidly making and breaking the circuit, or 
for reversing and alternating the current. A battery 
or some other generator is in circuit with this wire, 
which is termed the primary. 

When a current is passed through it, the iron core 
becomes a magnet, and attracting the hammer draws 
it away from the anvil and breaks the circuit. The 
iron core, then being no longer magnetized, releases 
the hammer, which falls on the anvil, and again closes 
the circuit, only to be reopened. This succession 
goes on with the highest rapidity. 

Sparking is prevented to a certain extent by the 
use of a condenser, which is a series of sheets of 
tinfoil, with paper interposed between each pair. 
Each alternate sheet of foil is connected to one and 
the other terminal of the primary coil. The charge 
which would produce the spark on breaking, rushes 
into the condenser to be at once discharged in the 



108 ELECTRICITY SIMPLIFIED. 

opposite direction through the coil, now on open cir- 
cuit. 

It is obvious that very rapid and violent disturb- 
ances of the lines of force and consequent ether waves 
follow this succession of makes and breaks. The 
disturbances are utilized by winding a second in- 
sulated wire over the core, directly over or next to 
the primary. At each ma*ke and break a pulse of 
current goes through the secondary coil, as the other 
one is termed. 

The primary coil in ordinary practice is made 
thick, with comparatively few convolutions. The 
secondary coil is then made of fine wire, and of a 
large number of convolutions, and of great length. 

The tension of the electricity in the secondary 
depends upon the ratio of its number of turns to 
those of the primary, the tension increasing with 
such number. 

This describes the general construction of the 
regular induction coil. There are several thiugs 
essential to the perfect operation and durability of a 
coil. The great point is good insulation. The 
secondary wire shows the strongest tendency to an 
escape of current from one convolution to another. 
The method of winding the secondary is sometimes 
such as to prevent this, the convolutions furthest 
removed in potential being kept also as far removed 
in position as possible. 

In the practical calculations employed by the en- 



CURRENT CONVERTERS. 109 

gineers of the alternating-current system the circuits 
are calculated as varying in tension directly as the 
relative number of convolutions of the primary and 
secondary, and the currents in the inverse ratio. 

If the primary wire is made very long, so as to in- 
clude many convolutions as compared to the second- 
ary, the secondary circuit will include a much lower 
potential difference, Thus the potential difference 
between the terminals where the primary current 
enters the coil may be one or two thousand volts, and 
the terminals of the secondary may only differ by 
fifty or a hundred volts. The ratio can be made 
anything. In alternate-current lighting a common 
reduction of potential is from one thousand volts in 
the primary to fifty volts in the secondary. In 
electric welding the reduction is many times greater 
than this. In both these cases there is no mechani- 
cal circuit breaker. The original current- is an alter- 
nating one and acts by induction upon the second- 
ary. The hammer and anvil or other make and 
break device is entirely omitted, the alternating cur- 
rent acting by itself. The lighting coils can be seen 
located on window sills and elsewhere on buildings 
supplied by the alternating current system of light- 
ing. They are termed converters. 



CHAPTER VII. 

THE GALVANIC BATTERY — THE ELECTROLYTE, AND 
THE LOCUS OF ITS POTENTIAL DIFFERENCE — 
POLARIZATION AND LOCaL ACTION — DIFFERENT 
EXAMPLES OF BATTERIES — THE ARRANGEMENT 
AND ACTION OF BATTERIES — STORAGE BATTERIES. 

The Galvanic Battery. The Electrolyte, and the 
Locus of Its Potential Difference. 

From a scientist's point of view, the electrostatic 
charge — that is to say, the charge held by a body — is 
of equal interest with the current. But as nearly all 
the great m'anif estations of electricity are due to cur- 
rents, the charge is apt to be thought of as something 
dry and unpractical compared with the manifesta- 
tions of electricity in motion or in current form. 
The two are related intimately, as has been shown in 
preceding chapters. 

The oldest familiar method of producing a current 
is by the galvanic battery. Accepting the contact 
theory, we may see how it explains the action of a 
battery. The simplest battery consists of two plates 
or pieces of different conducting materials immersed 
in liquid which acts more upon one than upon the 



THE ORIGINAL GALVANIC BATTERIES. Ill 

other. The plate most acted on is called the posi- 
tive, the other the negative, one. The original Volta's 
element consisted of a plate of copper and a plate 
of zinc immersed in dilute sulphuric acid. Unless 
special features are introduced or superadded, it is a 
very poor and inefficient battery. Yet it was with 
such an appliance that Sir Humphrey Davy performed 
his classic experiments upon the metals of the alkalies 
and produced the first voltaic arc. 

His battery had impure zincs and yielded large 
amounts of ill-smelling gas. From the first instant 
of immersion the bubbling and effervescing cups of 
dilute acid began to lose strength, and in half an 
hour probably were nearly exhausted, whether in use 
or disconnected. A modern battery would hold its 
strength for a long time if not used, and if doing 
work would not soon become exhausted. Sir Hum- 
phrey Davy never worked with an appliance rela- 
tively poorer than the great battery of the Royal 
Institution. It must have required very active work 
to immerse its many hundred plates, and get any re- 
sults from it before its strength was expended. 

There are a great variety of batteries. The pur- 
pose of these chapters will be best subserved by first 
taking into consideration a battery in which an acid, 
which may be dilute sulphuric acid, is the exciting 
liquid, and zinc, as in ninety-nine out of a hundred 
batteries, is the material of the positive plate. 

If the zinc is chemically pure, or if it is amalga- 



112 ELECTRICITY SIMPLIFIED. 

mated or alloyed with mercury, and if it is not in 
contract with the other plate no action that is visi- 
ble takes place. But if the plates are tested for 
charge, the zinc will be found to be of different 
potential than the copper. It follows that if in any 
way a discharge is effected, there will be thereby pro- 
duced a brief current. This can be done by bring- 
ing the plates into metallic contact. But on effecting 
this, which is usually done by connecting the ends of 
a wire to each plate, the discharge will not be in- 
stantaneous only, but will be continuous; in other 
words, a current will result. If elements enough in 
number and large enough are used, any conceivable 
current may be produced. It will produce the voltaic 
arc, or will melt the most infusible metals if they 
are made part of the metallic conductor or wire. 
Therefore a constant system of charging must take 
place. 

If the simple Volta combination is used, an effer- 
vescence, or escape of gas bubbles, from the surface 
of the negative plate will be observed. On collect- 
ing and examining these bubbles, they are found to 
be composed of the gas, hydrogen. . No action is dis- 
cernible at the positive plate of amalgamated zinc ex- 
cept a gradual diminution in weight and size. Theory 
can be applied to the battery action to explain what 
is taking place. 

The chemist on examining the battery finds that 
water is being decomposed. The oxygen of the 



CONTACT THEORY. 113 

water acts upon the zinc and oxidizes it, forming 
zinc oxide, which dissolves in the acid, causing the 
production of zinc sulphate and wasting of the 
plate. The hydrogen of the water goes to the copper 
and escapes from its surface as the bubbles already 
mentioned. Hence the battery is pulling apart 
oxygen and hydrogen, which have been in the most 
intimate contact, namely, in chemical or atomic com- 
bination. As the two are torn apart by the superior 
affinity of the zinc for the oxygen, they come oif op- 
positely charged with electricities, or differing in 
potential one from the other. This tearing apart of 
the two elements is continuously taking place as 
long as the plates are in metallic contact, so that a 
continuous discharge through the wire is effected 
or a current results. 

Water acidulated with sulphuric acid is a con- 
ductor. It might therefore seem to follow that the 
plates should discharge through the liquid of the 
element when the wire connection is not maintained. 
But the affinity of the zinc for oxygen, involving 
the holding of the water molecules in unstable equili- 
brium, maintains a difference of potential in spite of 
the watery conductor between. It so totally changes 
the conditions that no current whatever passes 
through the acid to discharge the plates, and, as far 
as any current may be supposed to go through the 
liquid, it is in the nature of a charging current. The 
liquid, while a true conductor and capable of acting 
8 



114 ELECTRICITY SIMPLIFIED. 

as such under proper conditions, becomes an electro- 
lyte in the battery and loses its power of simply 
conducting a current. 

It is not necessary to adopt the contact theory, 
which is now rejected by many authorities. We 
may assume that different elements carry individual 
and invariable quantities of electric charge. The 
zinc attracts the oxygen atoms, combines with them, 
thus setting free their charge, to be taken up by the 
surface of the zinc or positive plate. In an instant 
it becomes so highly charged that it repels the other 
atoms of oxygen. When the wire is connected it 
carries off this charge to the copper, and the zinc, be- 
ing discharged, is restored to a condition to attract 
more oxygen. 

The well-known diagram illustrates the action of 
the zinc and copper on the liquid in the battery. 
The oxygen keeps disappearing by combination with 
the zinc at one end of the battery; the hydrogen, 
by evolution as a gas, disappears at the other. At 
the same time the molecules keep exchanging atoms 
so that a constant travelling of the atoms from end 
to end of the liquid is kept up. In this way what is 
virtually a current goes through the water. It is 
perhaps, no current, properly speaking, the liquid 
simply effecting the continuous charging of the 
zinc with electricity opposite to that of the 
copper. 

Such a liquid is called an electrolyte, and this de- 



MOLECULAR ACTION 27V BATTERY. 115 

composition, which is exactly proportional to the 
current produced, is due to electrolytic conduction. 
Water, then, if not absolutely pure, can conduct 
electricity either as a regular conductor or electro- 
lvtically. A current may be caused to pass through 
it by immersing in a vessel of the fluid two terminals 




Fig. 27. 



or conductors coming from a battery or other source 
of electricity. If the difference of potential between 
the terminals is high enough, the water will be de- 
composed and will give off oxygen to one terminal 
and hydrogen to the other. The travel of the atoms 
in both directions takes place, and the water acts as 
an electrolyte. Whether a current goes through it 



116 ELECTRICITY SIMPLIFIED. 

or not, we have seen to be problematical. It is 
enough to believe that the oxygen atoms carry off 
the electricity opposite to their own, and that the hy- 
drogen atoms do the same for the reverse quality of 
electricity. If the difference of potential, on the 
other hand, between the two immersed terminals is 
low enough, no decomposition will take place, and a 
true current will go through the fluid, which acts as 
an actual conductor in such a case. 

The degree of difference of potential required for 
the electrolytic decomposition of every compound is 
absolutely fixed, and has been determined for a num- 
ber of substances. 

The knowledge of this quantity tells the difference 
of potential which the combination of the elements 
of these same compounds will develop in a battery. 
The potential difference required to effect a decom- 
position is the same as that developed by the com- 
bination of the same elements. The potential differ- 
ence is also precisely related to the heat produced by 
the same combination or to the heat required to 
effect the same decomposition. 

The difference of potential maintained between 
the opposite elements of a battery is generally re- 
ferred to its terminals or binding screws. It really 
should be sought at the active surfaces of the plates. 
The terminals may be at a determinably lower po- 
tential difference than the surface of the plates, al- 
though in almost all cases the difference is so slight 
as not to be measurable. 



POLARIZATION. 117 

Polarization and Local Action. Different Examples 
of Batteries. 

If the plates of a Volta's battery are connected by 
a wire, a current will go through it. But the cur- 
rent will very quickly weaken and in a few minutes 
will be so slight as to be almost useless for practi- 
cal purposes. The battery is said to be polarized. 
Polarization was the great trouble scientists of 
the days of Davy had to contend with in their bat- 
teries. 

Polarization in the electrical world is made to 
cover a multitude of sins. Properly it denotes in- 
terference, due to internal causes, with the proper 
action of a battery. In the case of the Volta's ele- 
ment the oxygen goes to the zinc and delivers its 
charge of electricity thereto and combines with it, to 
be dissolved on combining with the sulphuric acid 
radical. This leaves a fresh surface of zinc, so that 
there is no polarization there. If there were no 
acid in the water, then the surface of the zinc would 
become oxidized and would be no more attacked. This 
would be polarization, which is prevented by the 
acid. If we go to the other side of the battery we 
find the hydrogen collecting on the copper plate in 
minute bubbles and presently escaping therefrom 
and creating an effervescence in that portion of the 
liquid, the copper remaining coated with these 
bubbles. It is thus insulated from the electrolyte, 



118 ELECTRICITY SIMPLIFIED. 

the resistance of the battery is enormously increased, 
and it is polarized. 

Another interference is }3roduced by the hydrogen 
having a high affinity for oxygen. Instead of a cop- 
per-zinc couple we have to a certain extent a hy- 
drogen-zinc couple. The latter is of far lower electro- 
motive force. 

This hydrogen polarization is dealt with in various 
ways. In the Smee battery, which is a modification 
of the Volta battery, the hydrogen is given mechanical 
aid to escape. The negative plate is made of silver, 
coated with minutely divided platinum. The escape 
of a gas from a liquid is greatly facilitated by the 
presence of finely divided material. It seems to seek 
for points whence to start upon its upward journey. 
The platinized surface of the silver enables the hy- 
drogen to rapidly escape from the surface of the plate. 

In other batteries the same object is effected, also 
in a mechanical way, by agitating the solution or by 
constantly moving the negative plates. Sometimes 
air is blown through the solution which carries off 
the hydrogen. 

The chemical way of absorbing the hydrogen is 
more often employed. It consists in surrounding 
the negative plate with a solid or a liquid which com- 
bines chemically with the hydrogen. Such a liquid 
is dilute nitric acid, or a solution of chromic acid, of 
acidified potassium bichromate, or of acidified potas- 
sium permanganate. In Grove's battery the negative 



DEPOLARIZATION. 119 

element is platinum surrounded by dilute nitric acid 
as a depolarizer. In Bunsen's battery it is a piece of 
carbon in a depolarizing solution of sulphuric acid 
and potassium bichromate. 

In both these batteries it is an object to keep 
the hydrogen-absorbing or depolarizing liquid away 
from the zinc. At the same time the continuity of 
the liquid must be preserved or it will cease to act 
as an electrolyte. A cup or receptacle of porous 
material, such as earthenware, unglazed china, or even 
a parchment-paper bag, is used for this separation of 
liquids. The porous cup is placed within a glass 
one of considerably larger size, thus giving two com- 
partments. In one is placed the negative plate with 
its depolarizing solution; in the other the positive 
plate with the dilute acid. 

It will be evident that this is a very imperfect 
way of separating liquids. Diffusion inevitably goes 
on through the porous walls, but up to the present 
time it is about the best solution of the trouble. 
Electrolytic action is itself a species of diffusion. 

While diffusion of the electrolyte is thus a necessity, 
diffusion of the depolarizer is a defect. The latter 
trouble could be and is sometimes prevented by the 
use of a solid depolarizer. But the chemical action 
of a solid is so sluggish that batteries of this type, 
while they will eventually depolarize themselves for 
large quantities of electricity, quickly polarize when 
in action. They need periodical rest to recover their 



120 ELECTRICITY SIMPLIFIED. 

energy. Such are called open-circuit batteries, as 
being only suited for work on lines kept open or 
disconnected for most of the time. 

Leaving the hydrogen-producing battery, we may 
examine another combination incapable of this species 
of polarization. 

If the negative plate or electrode were hydrogen, 
it is obvious that there would be no hydrogen polar- 
ization. The Daniell battery uses a solution which 
instead of hydrogen deposits copper upon a copper 
negative plate, and hence it is free from hydrogen 
polarization. It contains a copper negative and a 
zinc positive plate. The copper plate is immersed in 
a solution of copper sulphate, the zinc in a solution 
of zinc sulphate. A porous cup is used to separate 
the two liquids. Under the action of the current the 
copper sulphate is decomposed. The copper is de- 
posited upon the copper plate, merely increasing its 
thickness, but not altering in any way its electrical 
position. The sulphuric acid radical combines with 
the zinc. In some copper sulphate batteries the 
porous cup is not employed, and the different 
specific gravity of the solutions is relied on to keep 
them separate (gravity battery). 

In the Daniell combination is found a good illus- 
tration of injurious local action. If the battery is 
left with the connection between the plates broken, 
or on open circuit, the copper sulphate diffuses 
through the rest of the liquid, and attacks the zinc, 



DEFECTS OF BATTERIES. 121 

dissolving it and depositing metallic copper upon it. 
This action is injurious as it wastes zinc and copper 
sulphate, and even tends to produce a species of po- 
larization. 

The Volta and Smee batteries are examples of single- 
fluid combinations, the others of two- fluid combina- 
tions. 

Sometimes, as has been said, solid depolarizers are 
employed. Thus in the Leclanche battery binoxide 
of manganese is the agent for disposing of the hy- 
drogen. The porous cup contains a carbon plate 
surrounded by a mixture of carbon in powder and of 
binoxide of manganese. The latter is reduced to 
sesquioxide by the hydrogen. The Leclanche battery 
is extensively used on " open-circuit work," in the 
telephone service and for bell-ringing. 

Other causes operate to impair the power of batter- 
ies. One is poor diffusion. The liquid directly be- 
tween the plates is acted on more strongly in the 
electrolytic way than any of the rest. Hence it is 
the first to be exhausted, and diffusion from the rest 
of the vessel has to replace it. This takes place 
rather slowly. Agitation of the liquid by mechanical 
means helps diffusion. The blowing air through 
the liquid, already mentioned, acts to facilitate diffu- 
sion as well as to remove hydrogen 

Some batteries are constructed with a view to' pre- 
vent diffusion so as to avoid local action. A jelly is 
often used to retain the electrolyte. Such are called 



122 ELECTRICITY SIMPLIFIED. 

dry batteries, and are adapted only for open-circuit 
work. 

The Arrangement and Action of Batteries. 

A cup of acid, with a plate of zinc and one of cop- 
per immersed in it, as we have seen, forms a battery. 
The ends of the plates projecting from the liquid 
are connected to the wire through which the cur- 
rent is to go. The current thus given is compara- 
tively weak. It may be increased by connecting more 
cups together. 

The exact function of a single couple should be 
clearly understood. It maintains a specific differ- 
ence of potential between the surfaces of its two 
plates or, what is the same thing, between the ends of 
the wire connected to the battery terminals. It also 
introduces a specific resistance which depends upon 
the nature of the solution and varies in amount in- 
versely with the facing areas of the plates and with 
their distance apart. Yet attempts to calculate this 
resistance by the specific conductivity of the solu- 
tion are not practically successful. 

Having a number of cells at our disposal we can 
halve the resistance of a single cell, without change 
of potential, by combining the two cells in parallel. 
This is done by connecting both negative plates 
together, as well as both positive. This gives us what 
is virtually a single cell of a battery, having the same 
electromotive force or potential difference, but only 



ARRANGEMENT OF BATTERY CELLS. 123 

one-half the resistance of a single cell. A third cup 
can be connected in parallel with the other two, 
which will give one-third the original resistance, with 
the same potential difference, and so on. 

If, on the other hand, it is the electromotive force 
that is to be increased, the cells must be connected 
in series. This is done by connecting the copper or 
carbon of one cell to the zinc of the other, the ends 
of the live wire or main conductor connecting one 
with the final negative, the other with the final posi- 
tive, plate. Two cells thus arranged will produce 
double the difference of potential, but at the same 
time will give double the resistance. 

The two systems may be combined in one battery. 
Thus, one pair in series may be placed in parallel 
with another pair also in series. To do this, two 
negative and two positive plates are connected right 
through, requiring four cells. This gives the resist- 
ance of a single cell and the electromotive force of 
two cells. 

The full investigation of the arrangement and 
number of cells for different purposes belongs to the 
subject of electrical calculations. It is enough to 
understand the role of the battery in general. It 
maintains a difference of potential between its op- 
posite poles, and introduces the hurtful element of its 
own resistance into the circuit. From this some 
curious conditions arise. If the minimum number 
of cells for a given current are required, the resistance 



VU ELECTRICITY SIMPLIFIED. 

of the cells must equal that of the external circuit. 
Suppose next that there are a number of cells placed 
in series but connected by a short, thick wire of prac- 
tically no resistance. Any number of cells may be 
added in series to those already there without giving 
any more current ; because as fast as the difference of 
potential increases, so does the resistance in the same 
ratio. 

If, on the other hand, the external circuit is very 
long or of high resistance, and the cells of the battery 
are arranged in parallel, any number may be added 
in parallel and the current will be increased only by 
a very minute amount. What is wanted in this case 
is higher electromotive force. The cells should be 
arranged in series. 

In either case the maximum current would be 
given by having the resistance of the battery equal 
to that of the line. The cells were arranged to the 
worst advantage possible in both supposed cases. 

TTe have seen in chapter IV. that electric work 
is measured in volt-amperes, or, if we follow out Ohm's 
law, is proportional to the current multiplied by the 
square of the resistance. This is deduced by alge- 
braic transformation of the original equation. From 
this proposition it follows that a battery does work in 
sending a current through a resistance. This resist- 
ance includes the entire circuit, battery and all. It 
follows also that any portion of the circuit receives a 
quantity of work proportional to its resistance. This 



CURRENT AND CIRCUIT. 125 

is because in a single circuit precisely the same cur- 
rent goes through every part of it at the same time. 
As only the resistance varies, the work expended on 
any part of the circuit is proportional to the square of 
the resistance. 

The fact that the current is the same in all parts 
of a circuit, although obvious enough, has more than 
once escaped apprehension by workers in electricity. 
Where a number of electromagnets are arranged in 
series on a circuit, as in automatic telegraph systems, 
to have them work evenly their resistance need not 
be equal. The number of convolutions must be the 
same, irrespective of resistance; yet it is on record 
that the error of supposing that the resistance was 
the controlling factor was committed by a profes- 
sional electrician. 

The circuit is composed of the wire or other con- 
ductor connecting the extremities of the battery, and 
of the battery itself. The current is generally, for 
convenience or as a matter of course, assumed to go 
through the battery. The battery in reality is work- 
ing as an electrolytic conductor, its resistance may be 
termed an electrolytic resistance, and cannot in 
practice be calculated with any accuracy as an ordi- 
nary resistance. The battery expends its energy on 
maintaining a difference of potential at its extremi- 
ties against the constant draught made upon this 
potential by the current. This difference causes a 
current to go through the wire. Meanwhile in all 



126 ELECTRICITY SIMPLIFIED. 

the battery cups the atomic migration of oxygen to 
zinc or positive plate and of hydrogen to carbon or 
negative plate, or some corresponding action accord- 
ing to the battery, is taking place. This amounts to 
a continuous resupplying of the charge taken from 
the positive to the negative plate by the wire of the 
external circuit. This travel of the atoms is as if a 
quantity of infinitely small receptacles of electricity 
were pouring out their contents into the j^lates of the 
battery. 

This conception, it will be seen, brings out the 
theory of electrolytic conduction by excluding the 
existence of a current properly so called within the 
battery, the battery acting as a replenisher of the 
electricity exhausted from the terminals of the battery 
by the wire connecting them. At the same time the 
atoms travel more or less easily according to the 
space they have to travel over and according to 
the cross-sectional area of their path. This varia- 
tion in ease of travel constitutes the variation in re- 
sistance of the battery. 

Given quantities of oxygen and hydrogen always 
deliver equal quantities of electricity to their re- 
spective poles. The conditions may be such that a 
higher or lower difference of potential is established 
and maintained at the terminals, but the current is 
exactly proportional to the oxygen consumed by the 
zinc or zinc consumed by the oxygen, according to 
the way we look at it, and the same for the other con- 
stituents. 



CONSUMPTION OF CHEMICALS. 127 

Thus, in a copper-sulphate battery (Daniell's, 
Gravity, etc.), if we weigh the copper plates before it 
goes to work and then take a current from it, we 
can determine what quantity of electricity its current 
delivered by weighing the same plates at the con- 
clusion of the time of action. Their increase of weight 
will be exactly proportional to the quantity delivered 
by the current, or to the coulombs or other unit of 
quantity. In like manner the zincs might be weighed, 
and their loss of weight would be proportional to 
the same thing. The copper sulphate expended 
might be determined with the same result. 

It must be understood that each quantity would be 
different, but that the quantity of each constituent 
would be proportional to the current in its own partic- 
ular ratio. 

Again, from another combination the same quantity 
of coulombs might be taken at nearly double the 
potential; yet the same quantity of zinc would be 
dissolved, notwithstanding the higher potential of 
the battery terminals. Consumption of chemicals 
corresponds to coulombs of electricity; difference of 
potential corresponds to relative chemical affinities. 

The law of electrolytes, as explained under the sub- 
ject of the chemistry of the current, applies accurately 
to the plates and solution of the electric battery it- 
self. If the current from a battery decomposes a 
given amount of an electrolyte in a separate vessel, 
the decompositions in the battery itself will be ex- 



128 ELECTRICITY SIMPLIFIED. 

actly in the proper ratio., depending on the atomic 
weights and valencies of the elements decomposed in 
the battery and in the electrolytic cell. 

Storage Batteries. 

An ordinary battery consists of a positive element 
attacked by the active solution, of a negative element 
unattacked thereby, and of some kind of depolarizer. 
The constituent parts are procured ready made from 
the chemical factory, zinc works, etc., and are in- 
troduced with water into the cups, and the battery is 
said to be set up. In use it runs down, the positive 
plate dissolves, the active solution and the depolarizer 
become exhausted, and after a while it has to be 
recharged. The old spent solutions are generally 
thrown away. 

If for the ordinary type of positive plates or ele- 
ment and for the depolarizer we substitute materials 
which can be produced in a cell by a galvanic current, 
namely, by electrolysis or electroplating, we have a 
storage or secondary battery. Where an ordinary 
battery is emptied and recharged, a storage battery 
is simply treated by passing through it a current in 
the direction opposite to that of its own natural cur- 
rent. After it has been exposed to the current it 
becomes electrolyzed. Upon one plate there may be 
deposited or formed the depolarizer, upon the other 
the positive material is formed and the exhausted 



STORAGE BATTERIES. 129 

solution in doing this is decomposed and restored to 
an active condition. When the charging current is 
stopped, and the battery is put to work, it delivers a 
current in a reverse direction to that of the charging 
current, and in doing so it gradually undoes the work 
which has been expended upon it. When its power 
runs down, it is again recharged and is again ready 
for work. 

This is the general mode of action of storage 
batteries. The favorite type is the lead-sulphuric acid- 
lead binoxide type. These consist of leaden plates 
for the elements. One set of plates, the negative 
ones, is chaiged with lead binoxide as a depolarizer, 
the other set with finely divided metallic lead as the 
positive element, and the solution is dilute sulphuric 
acid. 

The action is not yet perfectly settled, but in gen- 
eral is as follows: The spongy lead of the positive 
plates, when the current passes, is converted into 
lead sulphate. The hydrogen which goes to the 
negative plate is oxidized into water at the expense 
of the oxygen of the lead binoxide, and a difference 
of potential is thus established, which is used to pro- 
duce a current. 

It will be noted that no current would be produced 
by two plates of lead. The depolarizer or film of 
lead binoxide must be considered both negative 
plate and depolarizer. 

When the charging current is passed through the 
9 



130 ELECTRICITY SIMPLIFIED. 

solution, another action possibly comes in to re-enforce 
the above charging process. The negative plate may 
absorb and retain directly oxygen, and the positive 
plate may do the same for an equivalent quantity of 
hydrogen. Then in the use of the cell the hydrogen 
is consumed and the oxygen acts as a depolarizer. 

Grove's gas battery illustrates this last process 
perfectly. It consists of plates of platinum immersed 
in pairs in cups of dilute sulphuric acid and con- 
nected alternately like the regular plates of a battery. 
Of course no current passes when the circuit is 
closed. But if a current is passed through the solu- 
tion with the plates as electrodes, and due to a suffi- 
cient potential difference to decompose the water in 
the cells or cups, hydrogen accumulates on and in one 
electrode and oxygen on the other. On stopping 
the charging current, the battery is ready for action, 
and when connected a reverse current will be yielded 
by it. The hydrogen is the positive element, the 
oxygen is the depolarizer, and the platinum is the 
negative element. 

In point of time Grove's gas battery, which is a 
typical secondary battery, antedates all the present 
storage batteries, and was devised years before the 
name of storage or secondary battery was even thought 
of, and before any capitalist investigated the profits 
involved in the " storage of electricity." 

Secondary batteries, it will be seen, are merely con- 
trivances which substitute electrical for manual re- 



WEIGHT OF STORAGE BATTERIES. 131 

generation or recharging of their cells. Their success, 
as far as attained, is due to one circumstance — their 
possession of very low resistance. A primary battery 
cannot be made of as low resistance within the same 
compass. 

Their weight still is too great and militates strongly 
against them. The heavy leaden plates are but mas- 
sive skeletons for the support of very small portions 
of active material. While many other arrangements 
have been tried, at the present time the regular lead- 
plate combination is most used. 

The following figures are of interest in this con- 
nection. 

When energy is stored up in bent steel springs, 
about forty kilograms can be lifted one metre by the 
elasticity of a spring weighing one kilogram. 

When it is stored up in air compressed to one-sixth 
of its volume, about four hundred and sixty kilo- 
grams can be lifted in practice, one metre by one 
kilogram of air. 

When it is stored in storage batteries, about 3,370 
kilograms can be raised one metre by one kilogram 
weight of battery. (Abridged from Daniell's " Phy- 
sics.") 

This gives a ratio per unit weight in the three 
cases of 40 : 460 : 3370 or of 1 : 115 : 842 about, 
showing that there is room for improvement in dimin- 
ishing the weight of the storage battery. 



CHAPTEE VIII. 

DYNAMOS — MOTORS — TRANSMISSION OF POWER. 

Dynamos. 

Nothing in electric practice looks stranger to one 
unaccustomed to it than to see a whirling mass of 
wire, in contact with nothing but its bearings and 
the commutator brushes, act as the generator of a 
current that can illuminate a whole district of a city 
or do the heaviest kinds of electric work. The il- 
lustration of induction given in a preceding portion 
of this work contains the germ of a dynamo's action 
in a crude analogy. 

Suppose two electromagnets, one excited and the 
other passive, to be mounted face to face, one being 
arranged with mechanism so as to be quickly slid 
back and forth, toward and away from the other. If 
the stationary, or field magnet as it would be called, 
were kept excited by an independent current, and if 
the circuit of the other unexcited magnet were closed* 
then currents would be induced in the inactive mag- 
net as already explained, first in one direction and 
then in the other. The contrivance would be an 
alternating-current dynamo. 

While the current in the coils of the moving mag- 



ACTION OF THE DYNAMO. 133 

net would inevitably change in direction according to 
the way it was moving, whether toward or away from 
the stationary or field magnet, it is easy to imagine 
some subsidiary mechanism that would connect al- 
ternately the ends of the orcter circuit to opposite 
ends of the winding of the moving magnet — in one 
way when approaching, in the other way when re- 
ceding from, the field magnet. This would give pulses 
constant in direction but of varying intensity. The 
subsidiary mechanism is called a commutator. This 
arrangement would be a constant-direction-current 
dynamo. 

Another thing is obvious — that the outer circuit 
might include within it the winding or coils of the 
field magnet, so that the mechanism would produce a 
current without external aid. It would then be a 
self-exciting dynamo. 

Very rapid motion is essential to strong induction 
by the means described. It would be far easier to 
secure this by whirling the moving electromagnet 
around in front of the other than by reciprocating 
it. In practice rotation is invariably used. 

The moving coil of wire has to be wound upon a 
core of iron to entitle it to be called an electromag- 
net. The correct name for it is the armature. The 
purpose of the iron core is to concentrate the lines of 
force so as to give what is known as an intense field, 
and also for another reason: the iron core of the 
armature forms part of the magnetic circuit, and to 



134 ELECTRICITY SIMPLIFIED. 

avoid the expenditure of more energy than is re- 
quisite in maintaining lines of force through the 
circuit the reluctance of the circuit must be as low 
as possible. 

Of course a permanent magnet could be used as 
the field. In such case no energy would be expended 
on its excitation, and the last remark would not ap- 
ply so fully. Even in this case the lower the reluct- 
ance the better is the design. 

A rotating armature, a commutator, and a field 
magnet or magnets, called the field for brevity, are the 
three essentials of a constant-direction-current dy- 
namo. If the commutator is dispensed with, and a 
simple collector of any kind is used in its place, the 
three elements become substantially two, and we have 
an alternating- current dynamo. In these the field 
is usually excited by a separate source of current. 

Upon the shape and proportions of field, and of 
armature, and methods of winding, endless variations 
have been rung by different inventors. Generally 
the lines have settled down into a few typical forms. 
In practice these have to be varied to secure proper 
currents and proper potential difference at the ter- 
minals of the dynamo, all of which is the subject of 
mathematical calculation. 

It may be asked how a self-exciting dynamo is 
started. Iron that has once been magnetized always 
retains some of its mangetism. The fields of a dy- 
namo are always a little excited with residual mag- 



LARGE D Y1TA3I0S. 135 

netism, so that when the armature begins to rotate 
a slight current is at once induced in it. This 
strengthens the field, and the stronger field reacts in 
turn to increase the current, so that the normal 
strength is soon attained. 

Ordinary direct-current electric-lighting dynamos 
give from one hundred and twenty-five to one 
hundred and fifty volts potential difference between 
their terminals. But this is far exceeded in alter- 
nating-current lighting. In this country an average 
potential difference is one thousand volts. In Lon- 
don this has been also exceeded. The great Ferranti 
dynamos at the Deptford central lighting station 
maintain an average potential difference exceeding ten 
thousand volts. Each of these gigantic machines is 
of ten thousand horse-power. The armature core is 
in the shape of a ring thirty-five feet in diameter, 
and weighing with its shaft two hundred and 
twenty-five tons. The field magnets weigh three 
hundred and fifty tons. To the armature shaft are 
connected two 5,000 horse-power steam engines, one 
at each end of the shaft. The whole installation is 
the most colossal piece of electrical engineering ever 
erected. 

Motors. 

In describing a dynamo the armature has been 
spoken of as an electromagnet. If a current from 
an external source is passed into a constant-direc- 



136 ELECTRICITY SIMPLIFIED. 

tion-current dynamo, it will excite the armature so 
as to make it a magnet in reality, and will also ex- 
cite the fields. The current will enter at the ter- 
minals of the machine and will pass through the com- 
mutator into the armature. The relation of. parts is 
such that in doing this it will develop north and 
south poles in parts of the periphery of the arma- 
ture distant from the north and south poles of the 
fields. As like poles repel and unlike attract each 
other, the armature will at once turn a little to satisfy 
both the attraction and repulsion. But as soon as it 
has turned a short distance the action of the com- 
mutator shifts the current, and new poles are estab- 
lished in the armature back of the first and in the 
same relative positions which they at first occupied. 
The armature continues to rotate as the new poles are 
attracted and repelled, and after a few degrees of turn 
the commutator again acts as before, and shifts the 
poles back a little. This action goes on and the arma- 
ture continues rotating as long as current is supplied. 

It is evident that if there were no commutator, 
and if the armature had fixed poles, it never could 
rotate through a greater angle than one of 180°. 

The discovery that a dynamo is also a motor, or 
the discovery of the reversibility of the dynamo, is 
considered one of high importance. A dynamo is 
an apparatus for converting mechanical into electric 
energy. If electric energy is supplied, it can then 
convert that into mechanical energy. 



MOTORS. 137 

The reciprocating and utterly impracticable type 
of dynamo was used as an illustration of the principles 
involved in these mechanisms. It is impracticable 
because of the low speed with which it can be moved. 
But this objection does not apply to motors. A low- 
speed motor is very desirable, and the original motors 
were constructed on reciprocating lines. 

This reversibility of the dynamo brings about some 
curious results. If an electric railway is arranged 
with the motors on its different cars in series, rather 
an unusual arrangement, then, when a car is running 
down hill, its mQtor, instead of driving the car, is 
driven by it and becomes a dynamo, and sends cur- 
rent into the line. This helps to drive the other 
cars; so. that it is quite conceivable that on a line 
many miles might intervene between two cars, yet 
one running down a steep hill would pull the other 
one along the line and help to pull it up a distant 
hill. 

When a dynamo is generating current it absorbs 
mechanical energy. Hence the electric car in running 
down the hill and generating electrical energy has 
the mechanical energy due to its descent absorbed by 
the motor acting as a dynamo, so that a brake action 
is produced retarding the speed of descent. 

Thus two cars distant from each other may be as 
effectually connected in their movements by a slender, 
motionless wire as if they were attached to a traction 
cable. 



138 ELECTRICITY SIMPLIFIED. 

Transmission of Power. 

The transmission of power depends on the princi- 
ples enunciated especially in the preceding pages 
on batteries,, dynamos, and motors. The transmission 
of power by electricity involves : (1) A source of 
electric energy, generally a steam engine or water- 
wheel and dynamo, sometimes a battery; (2) a line of 
wire to act as conductor; and (3) a motor. These 
parts being given, the method is obvious. The dynamo 
generates electric energy, which appears in the cur- 
rent-potential form, and the current flows through the 
conductor. It reaches the motor, which may be 
many miles away, and causes it to rotate. From the 
motor, by any of the ordinary mechanical appliances, 
power is communicated to machinery. The ap- 
proved way of effecting the connections is to use 
two wires, one for the current of one direction, the 
other for the current of the other direction. 

By means of the lines thus connecting the source 
of electric energy and the motor, electric energy is 
transmitted at any desired rate compatible with the 
size of the wire and the admissible potential differ- 
ence or the current required. The rate of energy 
expended in a circuit and portion thereof is propor- 
tional to the maximum difference of potential within 
the limits multiplied by the current rate. If, there- 
fore, the generator produces a high potential differ- 
ence, less current will be required to give a specified 



ELECTRIC ENERGY TRANSMISSION. 139 

product of potential difference and current rate; which 
is the same thing as to give a specified rate of trans- 
mission of power. But the smaller current will heat 
a wire less ; therefore, the wire which can be used for 
transmission of a specified power may be made smaller 
as the motor works at a higher difference of potential. 
The size of the wire depends entirely on the current 
to be transmitted, and has nothing to do with the 
potential difference maintained at the ends of the 
wire considered by itself. 

Thus the entire energy of Niagara Falls could be 
transmitted through a common telegraph wire, ex- 
cept that the enormous differences of potential in- 
volved would make the current escape by every possi- 
ble avenue of leakage, and would make the system a 
menace to every one near it. The wire, however, 
as regards heating, would be unaffected. 

At the present time electric railroads are the most 
familiar examples of transmission of electric energy. 
In the usual style of electric tramway the dynamos 
at the station generate electric energy. One of the 
wires from the dynamo goes generally to earth. The 
other connects with the line, called colloquially the 
trolley wire, that runs along the road. Each car 
carries a motor, one of whose terminals connects with 
the trolley, and the other with the earth through 
the wheels and rails. The current from the dynamo 
follows the trolley wire, enters the car motor by the 
trolley, and, after passing through it, goes to earth. 



140 ELECTRICITY SIMPLIFIED. 

The cars on electric railroads are usually worked 
in parallel. If the line of wire and the earth 
beneath it be figured as two parallel conductors, the 
car motors are connected across from one to the 
other like the rungs of a ladder. The wire is made 
of such size as to have low resistance, keeping the 
potential difference between all parts of it and earth 
as nearly as possible the same, whether several cars 
are drawing upon it or not, and irrespective of what- 
ever distance may intervene between the respective 
cars and the central or power station. 

Cars are also worked on complete metallic circuit 
and in series, as already alluded to. They have at- 
tained a far more extended application in this 
country than elsewhere. 



CHAPTEE IX. 

THE TELEPHONE AND MICROPHONE — ELECTRIC 
LIGHTING — THE ELECTRIC TELEGRAPH — THE 
DANGERS OP ELECTRICITY — CONDITIONS POR 
RECEIVING A FATAL SHOCK. 

The Telephone and Microphone. 

A telephone may be considered a miniature 
motor and current generator, with a permanent field 
magnet. It is the simplest contrivance imaginable 
although productive of such astonishing results. It 
is a magnet X S consists of in a handle, around whose 
end a fine insulated wire H is wound, and close to one 
of whose poles, the one nearest the coil of wire, a 
plate of iron D is placed. If a momentary current is 
sent through the wire, the strength of the magnet is 
altered ; it may be increased or decreased according 
to the direction of the current through the wire. 
This alteration suddenly changes the attraction act- 
ing upon the iron plate, with the production of a 
noise due to the sudden change of pull ujDon and 
slight consequent motion of the plate. In this phase 
of its work the telephone represents a motor. 

The telephone also can act as a dynamo or as a 



142 



ELECTRICITY SIMPLIFIED. 



generator of current. This it does when spoken into 
and used as a transmitter. If the plate is moved 
suddenly the lines of force are affected and a cur- 
rent in one or the other direction is sent through the 
wire, assuming it to be on closed circuit. If two 
telephones are connected, and one of them is spoken 
into, its diaphragm, as the iron plate is called, is dis- 
turbed and a great number of pulses of current are 
produced. These act upon the other telephone and 




a 



& 




Fig. 23. — Telephones and Line 'with Earth Connections. 



cause its diaphragm to repeat the vibrations of the 
other one. But this involves the production of 
sound, and of the same sound which originally pro- 
duced the disturbance ; in other words, the telephone 
" speaks." 

In this, which is the simplest possible arrangement, 
the telephone which is spoken into is termed the 
transmitter, the other is the receiver. These roles are 
interchangable. The diaphragm is made of ferrotype 
plate, the same material on which ferrotype or "tin 
type " photographs are taken. 



THE MICROPHONE. 143 

The trouble with the arangement is the weakness 
of the actuating currents. This trouble is avoided 
by the use of the microphone, also a contrivance of 
the utmost simplicity, but one which is incomplete 
in itself, as it can do nothing without a telephone 
and a battery or other generator. The interest of 
the pair of connected telephones is that they are com- 
plete in themselves and are reversible. Either one 
can be transmitter or receiver in turn, which means 
generator and motor. 

To arrange a microphone circuit, one may place in 
circuit a battery, two blocks of carbon, such as the 
lead of lead pencils is made of, and a telephone. The 
two blocks of carbon must rest one on the other so 
as to form a very loose and easily disturbed contact. 
It is clear that every change in the nature of this 
contact will change the intensity of the current. If 
the blocks or the table they rest on is disturbed, even 
by being spoken at, the disturbances will produce 
minute changes in the current which will reproduce 
the disturbances and corresponding sounds in the 
telephone diaphragm. 

Of all substances carbon seems the best for the 
loose microphone contact, and is universally used. 
A great variety of microphones have been invented, 
almost all depending on loose carbon contacts. A 
simple form is shown in the illustration. In it C C 
are blocks of carbon between which a spindle of car- 
bon A is sustained in very loose contact. The base 



144 



ELECTRICITY SIMPLIFIED. 



X Y are the 



D serves to support the instrument, 
ends of the line wires. 

The mouthpiece in the ordinary telephone into 
which the transmitter of a message speaks is the front 
of a microphone. The instrument held to the ear is 
a simple telephone. The handle turned to ring up 




Fig. 29.— Microphone. 



the central office and the other subscriber actuates a 
small magneto -electric generator, which rings the 
bell, calls up the operator at the central office, and, 
when contact is made, rings the bell at? the receiver's 
instrument. 

The whole telephone system, it will be observed, 
represents one phase of the transmission of power. 



THE INCANDESCENT ELECTRIC LIGHT. 145 

Electric Lighting. 

When a current goes through a conductor, it heats 
it. The degree of heating depends on the resistance 
offered to the current and on the current's intensity. 
A given current will heat a conductor of small section 
to a high degree, while a large conductor will carry 
the same current without much rise in temperature. 
On this principle is based the incandescent electric 
light. The lamp consists of an exhausted glass globe, 
containing a filament of carbon of high resistance. 
The electric-light station, by means of wire of com- 
paratively large section, communicates with the ter- 
minals of the filament. The current heats the fila- 
ment to white heat, while the wire leads are almost 
unaffected. 

The lamps in the Edison and in most other house 
systems are arranged in parallel. This means that 
they are arranged between the leads, so that in a dia- 
gram they would represent the rungs of a ladder of 
which the leads would represent the sides. The 
electric station maintains a constant difference of 
potential between the leads, and the lamps are con- 
structed to work with that difference. 

In some cases, as for street lighting, the lamps are 
arranged in series so that the current goes consecu- 
tively through perhaps twenty, one following the other. 
Some device has then to be provided so that, if a lamp 
is broken or its filament fails, a by-pass or shunt for 
10 



146 ELECTRICITY SIMPLIFIED. 

the current shall be provided to keep the other lamps 
supplied, otherwise the extinction of one would mean 
the extinction of all. This objectionable feature is 
not found in the system of parallel connection. 

Sir Humphrey Davy, in 1801, working with the 
great (for those days) battery of the Eoyal Institution, 
found that on slightly separating the ends of a sev- 
ered electric conductor the current seemed to spring 
across the space. He employed pieces of charcoal as 
terminals. These became intensely heated, and the 
electric arc light for the first time shone upon the 
world. The battery contained 2,000 plates. 

This, in a few words, is the principle of the arc light 
now so extensively used for street lighting. By mech- 
anism worked by the current two carbon rods are 
kept at an almost invariable distance apart, ^ to 3 3 F 
inch, while the current is passing. If none passes 
they come in contact. This gives the conditions 
for an electric arc, which forms with attendant pro- 
duction of great heat and light. The carbons be- 
ing poor conductors of heat, the effect of the arc 
is concentrated near their ends, intensifying the 
light. 

Many variations of these two different methods of 
producing light by the current have been devised. 
and many modifications are in use. All the forms of 
electric light now in use belong distinctively to one 
or the other division. Those occupying a middle 
ground have not been extensively adopted. 



THE ELECTRIC LIGHT. 1-47 

The success of the electric light of the clay is 
due to the cheap generation of electricity by the 
dynamo. 

The alternating-current system depends upon the 
principle of the induction coil already explained. 
Alternating current is supplied from the central sta- 
tion through two leads, which are maintained at a 
high difference of potential. At points where light- 
ing is to be done, induction coils are placed whose 
primaries, wound with many coils of fine wire, connect 
the two leads. The secondaries of the coils are of 
fewer convolutions and of coarser wire, and to the 
latter the lamps are connected in parallel. 

The operation is simple. The alternating current 
passing through the primary induces in the second- 
ary a current of much greater amperage, but excites 
a much lower difference of potential in the terminals 
of the secondary. 

The induction coils, termed converters, may lower 
the potential from one thousand vclts between the 
terminals of the primary to fifty volts between the 
terminals of the secondary. This is a frequent type 
of reduction, but in the London installation the re- 
duction is many times greater than this. The con- 
verters are seen attached to the outside of houses near 
windows, or to electric-line poles. They vary in 
shape and details of construction, but the principle is 
outlined above. 



148 ELECTRICITY SIMPLIFIED. 

The Electric Telegraph. 

The modifications of telegraphs have been endless, 
but in this country at the present day, the Morse 
system is universally used. The elements necessary 
are: a battery or generator, a key to make and break 
the current for the person transmitting, and an elec- 
tromagnet with armature to act as a sounder for the 
person receiving the message. The armature is 
drawn back from the magnet by a spring. The key, 
battery, and magnet are arranged in circuit. If the 
key is depressed, the circuit is closed and the arma- 
ture is attracted, giving a click. When the key is re- 
leased the armature is jerked back, giving another- 
click. 

An alphabet has been devised based upon long 
and short depressions of the key, the famous dot and 
line alphabet, which enables the receiver of a message 
to spell out the message, by the ear, from the sound 
of the clicks. 

In a complete system each operator needs a key and 
a sounder. 

The Morse relay is what has made the success of 
the system. This is a magnet with armature, so ar- 
ranged that when the armature is depressed it closes 
a local circuit only a few feet long, which includes a 
strong battery and a sounder. Thus an exeedingly 
weak current, which will barely work the relay mag- 
net and will give very little sound, will operate the 



THE MORSE SYSTEM OF TELEGRAPHY. 149 

local circuit, producing a powerful sound from the 
sounder actuated by the local battery 

One of the curiosities of telegraphy is that the 
Morse system, now almost universally used by ear, was 
originally devised to print a message in lines and 
dots. A long strip of paper was drawn by clockwork 
through the receiving instrument, whose armature 
carried a stylus or writing point which was over or 
under and nearly in contact with the strip of paper 
passing through it. When the armature was at- 
tracted, and as long as held attracted, a mark was 
made on the paper. By manipulating the key in the 
distant office the armature was depressed and released 
as required, to spell out the message in Morse char- 
acters. 

After years of use some skilful operators acquired 
the power of working by ear, which at first was re- 
garded as a matter of curiosity or special interest. It 
was a long time before ear-receiving became the nor- 
mal method. 

A message can be received by the crudest possible 
methods. The line may be severed, and one end held 
above and the other below the tongue, and the pulses, 
so to say, tasted. Edward Everett Hale has written 
a very clever story founded on the reception of a 
Morse message by all of the senses. The printed 
message appeals to the eye, the sound to the ear, 
and a message can be felt by placing the fingers on 
the sounder or even relay magnet; tasting a mes- 



150 ELECTRICITY SIMPLIFIED. 

sage has been described already. The reception of a 
message on chemically treated paper such as used in 
Bain's chemical telegraph may produce an odor; and 
Hale tells in his ingenious story of a blind person 
smelling a message in this way. 

The Dangers of Electricity and Conditions for Re- 
ceiving a Fatal Shock. 

The deadly stroke of lightning is not easily pro- 
duced artificially. It is, if analyzed, the discharge 
of a very small quantity of electricity of enormous 
voltage or tension, and probably also of high amper- 
age. The amperage is high because the time of dis- 
charge is so very short. There is nothing incom- 
patible between a high amperage and small quantity 
or few coulombs, and both may refer to the same 
discharge. 

The static electric machines cannot conveniently 
be made to produce a discharge of this character, as 
it becomes unmanageable. Yet it would be easy to 
produce a fatal shock, but hardly with certainty 
every time. 

The development of electric lighting has shown 
that a fatal shock of much lower voltage than the 
lightning stroke can be given. It seems as if the 
amperage had something to do with it, although 
an intense current rarely goes through the body. 
Taking its resistance as one thousand ohms, some- 



EFFECTS OF DIFFERENT CURRENTS. 151 

thing about which there is nothing definite, it would 
follow that a single ampere of current will be fatal. 

The many fatal shocks received from electric-light- 
ing wires have usually been due to the discharge to 
earth through the body of a quantity of electricity 
urged by a potential difference nominally of five 
hundred or more volts. But it has been found that 
the character of the current makes a great difference. 
Dynamos produce currents of different characters. 
Some currents are almost uniform and in the same 
direction. These do little harm to the bodily system. 
Other dynamos produce what is termed a pulsating 
current, one always in the same direction, but vary- 
ing in intensity many times every second. Such a 
current is very severe in its effects. 

It will be observed that the voltage of the type of 
dynamos producing a pulsating current is always in- 
completely or wrongly stated. The voltage stated is 
the average, and includes maximum and minimum 
periods, so that the maximum may be greatly in ex- 
cess of the registered electromotive force. When the 
animal system is exposed to a pulsating current, this 
maximum voltage or electromotive force produces its 
full effect because a fraction of a second only is re- 
quired to produce death. 

The alternating current is most severe of all. Here 
the same points of excess of maximum over apparent 
Voltage obtains in still greater force. The proba- 
bility is at least indicated that the extreme variations 



152 ELECTRICITY SIMPLIFIED. 

of pulsating and alternating currents produce a def- 
initely destructive and shocking effect upon the 
nervous system. 

It is also undoubtedly the nervous shock that kills. 
Sometimes chemical decomposition of the vital fluids 
is suggested as a cause of death and injury, but there 
is little doubt that the shocking and fatal effects of 
a dynamo discharge are received long before any in- 
jurious chemical decomposition results from the tri- 
fling current passed. 

The general conditions for a fatal or severe shock 
from an electric-light system using the ground for 
the return circuit are these: The sufferer standing 
on the earth touches a bare spot on the wire, or some 
metallic body in electric connection with the wire. 
At once he receives, a shock of high voltage. If the 
circuit was in perfect condition no direct current 
could be received as it would not leave" the circuit. 
The utmost that could be received from a perfect 
circuit, would be comparatively little; enough in the 
case of an alternating current to give something of a 
shock, but hardly enough to kill, and burn the tissues 
at the points of contact. 

J^ext suppose that the system is imperfect, and that, 
at a point distant from the person touching the 
wire, the wire itself is in communication with the 
ground. Then a new element is introduced. Part of 
the current goes directly through the person's body, 
urged by an electromotive force higher or lower as 



CONDITIONS OF SHOCK. 153 

the " ground/' or the other point of connection with 
the earth, is more or less distant, and the shock 
varies in intensity with such degree of distance and 
with the consequent higher or lower potential differ- 
ence. 

A single "ground" upon a full metallic-circuit 
electric light or power system does not interfere to a 
perceptible extent with its working. But it keeps 
the whole line in a state ready to discharge a current 
through any one's body that may touch it. If the 
point of contact is near. the "ground" or point con- 
nected with the earth, a discharge of low voltage, and 
consequently not a severe one, is all that results. But 
if the " ground " is distant, then the high electromo- 
tive force comes into play and the shock may be fatal. 

Thus, suppose that a 1,500-volt dynamo is supply- 
ing a circuit including three thousand feet of wire 
with metallic return circuit, and assume the resist- 
ance to average the same at all parts. Suppose 
a ground to be established by any accident five hun- 
dred feet from the dynamo as measured on the wire. 
If then the wire was touched at its farther end, the suf- 
ferer would experience a discharge of nearly f gjgg of 
the total electromotive force or of twelve hundred 
and fifty volts. If he was but five hundred feet 
from the "ground," the discharge would be urged 
with but -jVVo 0I " the total, or two hundred and fifty 
volts. 

An electric-light system of high voltage, and of 



154 ELECTRICITY SIMPLIFIED. 

pulsating or alternating current type, on which a 
ground exists, is comparable to a powder magazine 
through which people are allowed to walk with 
lighted candles in their hands. Although but one 
person sutlers, yet his innocence and the utter ab- 
sence of contributory negligence make the majority 
of cases doubly sad. 

The alternating-current system has the high-ten- 
sion circuit for supplying only the primaries of its 
converters. Sometimes the converters become in- 
jured and are said to leak. . This means that the 
primary and secondary are in metallic or good elec- 
tric contact. In such a case the secondary circuit, 
which is the house circuit, participates in all the 
dangers of a distant "ground." 

It follows that " grounds " are to be watched for 
most vigorously by electric-station superintendents. 
If the station supplies alternating current, then con- 
verter leakages have also to be watched for. It 
is not alone death that is involved, but fire also. 
A distant earth connection followed by a second one 
through a wire or other conducting object in contact 
with inflammable material may bring about a confla- 
gration. 

It is easy to ask for safeguards against these evils. 
Such provisions must come largely from the engineer- 
ing department of the electric companies. The mis- 
fortune is that the negligence of one concern may do 
injury to others, and the innocent may suffer in place 
of the guilty. 



IXDEX 



PAGE 

Action, local 120. 121 

Alternating-current lighting.. . 147 
Alternating lighting S3'stem 

converters 109 

Ampere 63, 87 

Amperean currents of earth ... 90 
Amperean theory of magnet- 
ism 87 

Amperemeters 93 

Analogy between electric and 

magnetic circuits *r. 100 

Analogy, hydraulic, of circuit . 40 
Analogy, hydraulic, of current 39 
Analogy, hydraulic, of electro- 
static and electromagnetic 

relations 59, 60 

Analogy, mechanical of a cir- 
cuit.." 67,68,44,45 

Analogy, mechanical, of elec- 
tromagnetic lines of force ... 77 
Analogy of ampere ; the 

miner's inch 63, 64 

Analogy of line of force 83 

Anode 73 

Armature 133 

Armature,attraction of magnet 

for 100 

Arrangement of batten* cells. 

122-124 
Atlantic cable, time required to 

transmit a signal through .... 53 
Attraction due to ether stress. 97, 98 
Attraction of magnet for arma- 
ture 100 

Attraction of oppositely ex- 
cited bodies 28, 29 

BATTERiES,arrangementof. 122-124 
Batteries, open-circuit — 119,120 

Batteries, storage 128-131 

Battery, consumption of ma- 
terial in 127 

Battery, contact theory of 113 

Battery, defects of original ... Ill 



PAGE 

Battery, different kinds of. 118-120 
Battery, potential difference 

in 127 

Battery, resistance of 126 

Battery, the galvanic 110 

Bubbles from battery 112 

Calorimeter 69 

Capacity depends on surface . . 22 

Capacity, how affected 24 

Carbon in microphone 143 

Cathode 73 

C. G. S. units 14 

Charged body 20 

Charge, electric 20-24 

Charge, electric, resides on sur- 
face 20 

Chemistry and electricity cor- 
related 28 

Chemistry of current 69-75 

Circuit-breaking device 107 

Circuit, closed, necessary for 

current-induction 104 

Circuit, current in 125 

Circuit, hydraulic, analogy of. 40 

Circuit, magnetic 82, 83, 99 

Circuit, open and closed 39 

Clerk Maxwell's theory 60 

■•Clockwise' 1 direction of cur- 
rent 87,88 

Closed circuit 39 

Coil induction 105-109 

Coil, spark 106, 107 

Commutator 133 

Condenser 24 

Condenser of induction coil, 107, 108 

Conductance 48 

Conductor 23 

Contact action 29 

Converters for alternating cur- 
rent work 109, 147 

Copper, polarization of 117 

Coulomb 6.3 

Current, chemistry of.. 69-75 



156 



INDEX. 



PAGE 

Current, electromagnetic unit 

of 56, 57 

Current, electrostatic unit of . . 55 

Current in circuit 125 

Current-induction 95-105 

Current, its direction 26 

Current, how produced and 

transmitted 38 

Currents, parallel, action on 
each other 96, 97 

Daniell battery, standard of 

voltage 62, 63 

Davy's, Sir Humphrey, bat- 
tery Ill, 146 

Death by electricity 150-154 

Decomposition of water 70-73 

Depolarizers, solid and liquid, 

118.119 

Diagram of lines of force 79 

Diagram of work and energy 

in a circuit 66, 6? 

Diagrams of falls of potential 

in circuit 47-49 

Dielectric 23 

Dielectric, function of, in a 

switch 42 

Difference of potential 21 

Dimensions of units 14 

Direction of a current. 26 

Double fluid theory 27 

Dynamic and static electricity. 13 
Dynamo, great, in London. . . . 135 

Dynamo, reversibility of 136 

Dynamos 132-135 

Dyne 14 

Earth a gigantic magnet 90 

Earth as part of circuit 40-41 

Earth, as reservoir of electric- 
ity 21 

Earth coil 91 

Earth currents 90 

Earth, its lines of force 90, 91 

Earth, polarity of, byAmpere's 

theory 88-90 

Efficiency of circuit 68, 69 

Efficiency of electric generator, 46 

Electrically charged body 20 

Electric charge 20-24 

Electric charge resides on sur- 
face 20 

Electricity and chemistry cor- 
related 28 

Electricity, fatal effects of. 150-154 



PAGE 

Electricity, origin of name 19 

Electricity, pdsirive and nega- 
tive 25-29 

Electricity, static and dynamic. 13 

Electric machine, f national 35 

Electric waves 12,13 

Electrodes 73 

Electrolysis 72, 73 

Electrolysis in battery 114 

Electrolyte in battery 114 

Electrolyte, its quality and ac- 
tion 69, 70 

Electromagnet 86, 87 

Electromagnetic and electro- 
static lines of force 76 

Electromagnetic and electro- 
static units, relations of.. . . 57-60 
Electromagnetic induction, im- 
portance of . . . 95 

Electromagnetic lines of force, 

76-86 
Electis«magnetic lines of force, 

how mapped out 78, 79 

Electromotive force, electro- 
static unit of. 55 

Electromotive force present 

everywhere in a circuit 45. 46 

Electroplating 74, 75 

Electrostatic and electromag- 
netic fines of force 76 

Electrostatic and electromag- 
netic units, relations of .. . . 57-60 
Electrostatic lines of force.. . 29-32 

Electrostatic units 54, 55 

E. M. F., its meaning 43 

Energy 15 

Energy and work, electrical. 65-69 

Energy, available 16 

Energy, by induction 94 

Energy, conservation of 15 

Energy, examples of trans- 
formation of 17 

Energy expended on conduc- 
tors 46 

Energy, how stored 131 

Energj", kinetic 16 

Energy, potential 16 

Energy, radiant 13 

Energy, transformation of 15 

Energvand work, unit of rate 

of... 68 

Equator, magnetic 91 

Erg 15 

Ether, its part in producing a 

current 42 

Ether, luminiferous 9-13 



INDEX. 



157 



PAGE 

Faraday's work 76 

Field 132-134 

Field, magnetic . . . -. 99 

Force 14, 15 

Force by induction 94 

Force defined 14 

Force, lines of, a metaphor 

only 105 

Force, lines of, electromag- 
netic 76-86 

Force, lines of, electrostatic. . . 32 

Force, radiant . . 11, 13 

Franklin's theory 26, 27 

Galvanometers 93 

Gas battery a storage battery . 130 

Heat of decomposition of so- 
lutions 116 

Heliograph 50 

Hydrogen as positive element 
in a battery 118 

Hydrogen from battery 113 

Induction coil 105-109 

Induction coil, condenser of, 

107, 108 

Induction coil, primary and 
secondary of 108 

Induction, electrostatic and 
electromagnetic 94 

Induction, electromagnetic, im- 
portance of 95 

Induction of currents 95-105 

Jar, the Leyden 32-37 

Lamps, arc. 146 

Lamps, incandescent 145 

Lamps in parallel and in series. 145 

Lenz's law 104. 105 

Leyden jar 32 37 

Lighting, incandescent 145 

Light, velocity of 12, 60 

Line of force, a term of con- 
venience 77 

Lines of force, a metaphor 105 

Lines of force, electromag- 
netic 7G-86 

Lines of force, electrostatic. 29-32 
Lines of force, how mapped 

out 78,79 

Lines of force of earth 90, 91 

Lines of force, their direction . 84 
Lines of force traced by a com- 
pass 81 

Luminif erous ether 9-13 



PAGE 

Magnet and perpetual motion, 85 

Magnet, electro- 86, 87 

Magnet, how acted on by cur- 
rents 92, 93 

Magnetic circuit 82, 83, 99 

Magnetic field 99 

Magnetism, Ampere's theory 

of 87 

Magnet not a seat of energy, . . 85 

Magnet, origin of name 89 

Magnets 84-92 

Magnets formed by induction. . 92 

Mass 17 

Mercury column standard ohm. 63 

Microphone 143, 144 

Motors 135-137 

Negative and positive electric- 
ity 25-29 

Ohm 63 

Ohm's law 43 

Open circuit 39 

Permeance of air 80 

Permeance of iron, nickel, and 

cobalt 80 

Perpetual motion and magnet, 85 

Polarity of lines of force 76 

Polarity of magnet dependent 

on direction of current 87 

Polarization 117 

Polarization, chemical treat- 
ment of 118, 119 

Polarization, mechanical treat- 
ment of... 118 

Poles, magnetic 91, 92 

Poles, why magnet points to. 88-90 

Pole, unit magnetic 57 

Positive and negative electric- 
ity 25-29 

Potential, diagrams of fall of, 

in a circuit 47-49 

Potential difference, 21 

Potential difference in battery. 127 
Potential difference required 

for decomposition 115 

Potential difference, seat of, in 

battery ... 116 

Potential difference, the cause 

of a current 42 

Potential of earth 21 

Potential, zero of 25 

Porous cup 119 

Power, transmission of 138-140 

Primary of induction coil 108 



158 



INDEX. 



PAGE 

Quantity, electromagnetic 

unit of 57 

Quantity, electrostatic unit of, 

54, 55 

Radiant energy 13 

Radiant force 11-13 

Railway, electric 137-140 

Relations, electrical 19 

Reluctance 98, 99 

Repulsion due to ether stress 97, 98 
Repulsion of similarly excited 

bodies 29 

Resinous electricity 25 

Resistance, electrostatic unit 

of 55 

Resistance, its action 43 

Resistance of generator and 

outer circuit 46 

Ring, vortex 84 

Secondary of induction coil. . . 108 

Single-fluid theory 26, 27 

Smoke ring, analogue of line 

of force 83 

Soldering, electric 74, 75 

Solutions, electrolysis of 73 

Spark coil 106,107 

Sparking of telegraph instru- 
ments 107 

Specific inductive capacity 24 

Static and dynamic electricity. 13 
Storage batteries 128-131 

Telegraph 148-150 

Telegraph messages, different 

ways of receiving 149 

Telegraph signal, velocity of 

its transmission 51-53 

Telephone 141-143 

Tension in a Ley den jar 34 

Tension, high 22 



page 
Transmission of power in tele- 
phone system 144 

Trolley wire 139 

Units 14 

Units, practical 60-65 

Velocity of electricity 49-53 

Velocity of light 60 

Velocity of transmission of an 

electric impulse 43, 44 

Vitreous electricity 25 

Volt-coulomb, a compound 

unit of work and energy 66 

Voltmeters 93 

Volt 61, 62 

Water as conductor or electro- 
lyte 115 

Water, decomposition of 70-73 

Water-drops, their change in 

capacity . . . : 23 

Waves, electric 12, 13 

Waves of electricity 50 

Weight ; 18 

Weight of storage batteries.. . . 131 
Welding, electric, converters in 109 
Wires, parallel, action when 

carrying currents 96, 97 

Wire through which a current 

passes a seat of energy 44 

Work 15 

Work and energy, electrical. 65-69 
Work and energy, unit of rate 

of 68 

Work, reciprocal of energy 16 

Zero of potential 25 

Zinc, amalgamated, in battery 112 
Zinc, chemically pure, in bat- 
tery ".. 112 

Zinc, polarization of, in bat- 
tery 117 



The Improved Double Cylinder Law Battery. 

Covered by Letters Patent, infringement of ichich will be prosecuted. 




THIS Battery has been brought to a high state of perfection. Perfectly uni- 
form and reliable in action? Of faultless construction and beautiful ap- 
pearance. In these respects it is unapproached. Its electromotive force is 
1.5 volts, and its internal resistance .5 of an ohm at the start, an 1 continues the 
same until the zinc is consumed or solution exhausted. At this date, Oct. 1st, 
1891, it has been on the market for eleven years, and tens of thousands are 
now in use throughout the length and breadth of the land. Cells put in use 
in t88i are still working, and working as well as at their start ; nothing but 
the zinc and the solution, costing but a few cents, ever having been renewed. 

In all porous-cup and other forms of batteries which require the periodical 
renewal of the negative element, the first cost of the cell is insignificant as 
compared with the cost of the renewals. 

The sale of these perishable negative elements is the chief source of profit 
to the makers of the batteries in which such elements are employed. The 
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or question on the point the Law Company will at any time, and without 
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LAW TELEPHONE COMPANY, Sole Manufacturers, 

85 JOHN STREET, NEW YORK. 



Cable Address, BARBERRY. 



WK. A. CHILDS, President. 



Hi Insulation of Electric Wires m 



The question is sometimes asked, " What is insulation?" 

The word insulate means generally to isolate or separate, but 
in ELECTRICITY it means to CONFINE the current to the 
conductor. 

In a perfectly dry atmosphere, a covering of cotton, silk, or 
other fibre answers the purpose, especially for low-tension cur- 
rents such as used for annunciators, telephones, etc.; but all 
fibrous materials absorb moisture and thereby become conductors, 
and therefore none of them are safe for the insulation of ELEC- 
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